The only way you can do that is with a blockchain.info wallet, correct? I know you can send from a specific address, but on QT and multi bit, if there is a way to send with a specific address, please share...
Dunno. I know with Electrum, I can freeze specific addresses, as well as mark addresses as "prioritize"...
I guess the other option is to export the key in question, import it into a new, virgin wallet, and work from there.....
grnbrg.
PS: Yeah, ok, not all clients allow signing... My 'droid wallet doesn't, for example. And if you entered an exchange deposit wallet, that's a problem as well...