menu nicklist {
DCC Send:customsend $1 $$?="Enter path\filename"
}
alias customsend {
dcc packetsize 4096
dcc send $1 $2-
}
Something like that would work. Then you'd right click a nick, select DCC Send from the menu, and enter the filename. Of course, you can make it more useful by using a file selection dialog rather than just an input event, but that gives you an idea.
EDIT: Btw, I also think changing the default in that dialog is a good feature. This is just a way to make it work in the meantime.