The RAM drive is a simple registry setting

“HKLM\System\CurrentControlSet\Services\RamDrive\Parameters\Disksize”

 

My suggestions is:

1. Manually change the RAM drive to 512MB on a test machine

2. Capture the registry settings via HPDM

3. Deploy the captured registry to another test thin client and see if it works.

 

Then Deploy the registry to rest of your thin clients.