Kelly: First I need to thank all of my more-technical cohorts for their answers to this... :)
As it turns out, the answer is yes, you can restrict OWA to offering only OWA Light for a specific Virtual Directory (vdir) or for a specific user.
To set the restriction on the Virtual Directory for all users, you make the following call in PowerShell:
Set-owavirtualdirectory –id:<id of virtual directory> -PremiumClientEnabled:$false
To set it for a particular user, you could call:
Set-CasMailbox –id:<id of mailbox> -OWAPremiumClientEnabled:$false
It is worth noting that even if this bit is set, the user will still see both the "Premium" and "Light" logon options. However, they will always get the Light experience, regardless of which option was chosen. The reason for this is because per-user segmentation over-rides the per-vdir segmentation, and when we render the logon page we don't know who the user is yet.
Glad to hear you’re using OWA Light! Is the “availability stuff” that you’re referring to the Free/Busy Grid on the Scheduling Tab?