This is not a perfect solution but you could try something along this line.
Assuming the computers have 1 physical disk and a single system partition, are working on a workgroup (domain would be ok also) and you do not need a forensic level wipe (I.E. overwrite each and every bit to prevent data recovery)
1. Use disk management to shrink the system partition and create a second partition and assign drive the D: drive.
2. Use local GPO to hide the C: drive (note this is not 100% secure but OK for a quick fix).
3. Invite Users to use the D: drive for their data downloads etc.
4. Use logon/logoff scripts to wipe the D: Drive on logon or logoff. quickest way to wipe would be to use 'Format d: /q /x /y'.