Newbie here...

You can first mount the ISO and then connect a drive letter to this, and I wrote this script for that:

#Requires -RunAsAdministrator
param (
  [Parameter(Mandatory = $true)][String]$ISOFileName,
  [Parameter(Mandatory = $true)][String]$DriveLetter
)

#Check if DriveLetter is in use
if (Test-Path -LiteralPath "$($DriveLetter):") {
  Write-Warning ("Specified driveletter {0}: is in use, exiting..." -f $DriveLetter)
  return
}

#Check if $IsoFileName was already mounted
if ((Get-DiskImage -ImagePath $ISOFileName).Attached) {
  Write-Warning ("ISO {0} already mounted, exiting..." -f $ISOFileName)
  return
}

#Mount first
if (Test-Path -LiteralPath $ISOFileName) {
  try {
    $Mount = Mount-DiskImage -ImagePath $ISOFileName -NoDriveLetter -StorageType ISO -Access ReadOnly -ErrorAction Stop
  }
  catch {
    Write-Warning ("Error mounting {0}, exiting..." -f $ISOFileName)
    return
  }
}

#Assign driveletter
try {
  mountvol.exe "$($DriveLetter):" $($mount | Get-Volume).UniqueId
  Write-Host ("Mounted {0} at {1}:" -f $ISOFileName, $DriveLetter) -ForegroundColor Green
}
catch {
  Write-Warning { "Error mounting {0} at {1}:, dismounting {2}" -f $ISOFileName, $DriveLetter, $ISOFileName }
  try {
    Dismount-DiskImage -ImagePath $ISOFileName -ErrorAction Stop
    Write-Host { "Dismounted {0}..." -f $ISOFileName }
  }
  catch {
    Write-Warning ("Error dismounting {0}, Check Diskmanagement" -f $ISOFileName)
  }
}

Save the script to c:\scripts, as mount-iso.ps1, for example. Then run it as Administrator, as c:\scripts\mount-iso.ps1 -ISOFileName c:\data\iso\isofilename.iso -DriveLetter X to mount c:\data\iso\isofilename.iso as X:\