If you are putting up with computer-generated QRM during a contest
anyway and you're not a die-hard real key fan you might as well con-
sider generating the CW directly from keyboard input. This will
do away with the key-up problem you mentioned and eliminate sampling
altogether. (The sampling rate requirements for CW are not that high,
and if your computer doesn't have anything else to do during a contest,
fine, but mine is networked, so I won't be able to tell in advance ;)
and a non-real-time multitasking OS just isn't born for sampling
applications.)
Typing on the keyboard during a contest can actually be pretty useful
because you can write down whatever you hear much more quickly and
you don't have to worry about sloppy handwriting later on ;)
Kai