Sure. You could assign a unique value to each user & ensure it's in the
querystring, cache the user control to varybyparam, then your user controls
would get cached per user.

You can also use outputcache & varybycustom & write your own getvarybycustom
function to vary by user (IP? unique ID in cookie? something

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/c
pconOutputCache.asp).

You could also cache data/etc for the user in session, & just rebuild the
control from that data each time. You didn't say where the performance issue
was, so session storage may not be appropriate.