The NT idea won't work with '95.

You might go further and hide it so that even if it's accidentally left on-disc it is unlikely to be found.

To give you an example...
E.g. copy notepad.exe to (say) z.zzz
Copy a (say) .txt file and name it (say) y.yyy
Double-click on the y.yyy file and when asked to Open With... choose Other and select z.zzz

You can check the registry to see what settings are added and mimic them. ShellExecute() should run it successfully (not tested though).

Just an idea, it might work.