Yea, I'll second what the previous two guys said... It's a bitch to remove the dash on a Supra and change the tweeters PROPERLY.
I have seen individuals that have broken the tweeter mounts by pushing them down and after installing new tweeters, epoxy the stock tweeters back to their original mount. It's kinda "ghetto" if you ask me but I have seen it done and if done right they can not be distinguished from doing the remove the dash method.
Want easy? Put em' like the others have said....In the kicks or on the door.
Good luck with whatever you decide to do.
San Antonio, Texas