May we assume Gaim's isn't the only "URGENT" window you want to do this for. If Kopete generated one you would want to unhide Kicker for that. I use Kopete as my example because if the IM client were your only concern, then you could switch to Kopete & proceed as suggested.
Meanwhile, some more info., please:
- Which distro?
- Which ver. of KDE?
- What solutions have you tried & discarded?
- Is there no option for this in Kcontrol?