putty pageant - forget keys after period of inactivity

in the environment where windows client computers are used to run putty to connect to multiple linux servers i'm considering moving away from password based authentication and using public/private key pairs with pass-phrases.

using ssh-agent would be nice, but at the same time i'd like it to 'forget' the pass-phrases after given period of inactivity.

it seems that putty's pageant does not provide such feature; what would you suggest as alternative? solutions that i'm considering:

• patching pageant code [might be tricky, code is probably quite rusty and project - sadly - stagnant]
• writing small custom application using GetLastInputInfo and killing pageant if the machine was idle for more than let's say 15 minutes [ yes, there'll be separate policy for locking the desktops as well ]
• using alternative ssh client and ssh agent. any suggestions?

thanks!