Bulk Update SharePoint Online User Profile Properties with Extension Attributes in Azure AD

I have been using the following script to bulk update custom SharePoint Online User Profile Properties with Azure AD attributes that aren't mapped to SharePoint by default (Azure AD gets information from our on-premises AD via Azure AD Connect). It iterates through each Azure AD user, captures their attributes, then uses Connect-PnPOnline to bulk update SharePoint with a JSON file that has extracted specified Azure attributes.

This works great for standard Azure AD attributes such as Mobile or Department, but I cannot get this to work with Extension Properties (on-premises AD attributes that are synced to Azure AD as Directory Extensions in Azure AD Connect, in this case the IP Phone and Notes fields in AD).

#Function to Extract User profile Extension Property
Function Extract-ADUserProperties
{
    Param ([Parameter(Mandatory=$true)][string[]]$ADProperties, [Parameter(Mandatory=$true)][PSCredential]$Cred)
  
    Try {
        #Connect to AzureAD
        Connect-AzureAD -Credential $Cred | Out-Null
  
        #Get All Users from AzureAD
        $AllUsers = Get-AzureADUser -All:$True
        Write-host "Total Number of User Profiles Found:"$AllUsers.Count 
        $UserProfileDataColl = @()
  
        #Iterate through All User profiles
        $Counter = 1
        ForEach($User in $AllUsers)
        {
            $UserProfileData = New-Object PSObject
            $UserProfileData | Add-Member NoteProperty IDName($User.UserPrincipalName)
 
            #Get Value of each property of the user
            ForEach($ADProperty in $ADProperties)
            {
                #Get User Profile Property value
                $ADPropertyValue = $User | Select -ExpandProperty ExtensionProperty $ADProperty
                If(!$ADPropertyValue) {$ADPropertyValue = [string]::Empty}
                $UserProfileData | Add-Member NoteProperty $ADProperty($ADPropertyValue)
            }
            $UserProfileDataColl += $UserProfileData
            Write-Progress -Activity "Getting User Profile Data..." -Status "Getting User Profile $Counter of $($AllUsers.Count)" -PercentComplete (($Counter / $AllUsers.Count)  * 100)
            $Counter++
        }
        #Convert data to required Json format
        $JsonData = $UserProfileDataColl | ConvertTo-Json
        $JSON = @"
        { "value":
            $JsonData
        }
"@
        #Export JSON to a File
        $JSON | Out-File -FilePath $Env:TEMP/UserProfileData.JSON -Force
        Write-host "Extracted user profile Properties Successfully!" -f Green
    }
    Catch {
        write-host -f Red "Error Getting User Profile Properties!" $_.Exception.Message
    }
}
 
#Call the function to Extract User profile data to JSON
Extract-ADUserProperties -ADProperties @("extension_cc64416229824d08b7a6db3c5ea9b847_ipPhone", "extension_cc64416229824d08b7a6db3c5ea9b847_info") -Cred (Get-Credential)
 
#Parameters
$SiteUrl = "https://tenant.sharepoint.com"
$SiteRelativeFolderPath = "/Shared Documents"
 
#Connect to site
Connect-PnPOnline $SiteUrl -Credentials (Get-Credential)
 
#Call the Bulk Import Job - Mapping in format AzureAD User Attribute = SharePoint User Profile Property
New-PnPUPABulkImportJob -Folder $SiteRelativeFolderPath -Path $Env:TEMP/UserProfileData.JSON -IdProperty "IdName" -UserProfilePropertyMapping @{"extension_cc64416229824d08b7a6db3c5ea9b847_ipPhone"="ipPhone";"extension_cc64416229824d08b7a6db3c5ea9b847_info"="info"}

With standard Azure AD attributes like "Country" and "Mobile", I get a nice clean JSON file like this:

But when I try to use Extension Attributes, which are all contained within the "ExtensionProperty" Azure AD attribute, I get the following:

When what I'm really wanting is to be pulling just the two extension attributes, which would ideally result in a JSON file like this:

Any ideas on how to modify the script to achieve this behavior? I'm thinking that the following probably needs to be used, but I'm not sure how best to incorporate this into the script.