If I remember correctly you set the number of logins to keep on the core server under configure services, so I'm not sure that you could change that for only a handful of devices.
You might be able to manipulate the local inventory though. As the logon history information is stored in the registry under HKEY_LOCAL_MACHINE\SOFTWARE\LANDesk\Inventory\LogonHistory\Logons key, you might be able to clear this out then run an inventory scan to see what the Primary Owner is set to. If it gives you what you want (blank would be ideal) then you could write a script that you run on those PCs that would clear this out. You would probably want it to run just before your inventory scan is run. That way there would be no login history to scan.
I have not tested this but it might point you in the right direction.
Does anyone from LANDesk see an issue with doing this?