You can drive without the slave cylinder if you really have to. I've had to do it a few times. You look like a tool though when you start the engine in first at the lights and the car kangaroos forward. Then it's just a case of rev matching to change up and down the box. You'll get a couple of crunches until you get used it. Try not to stop, so plan ahead and slow for things as much as possible. If you have to stop, knock the engine off, into first and then start it in 1st and off you go again.
But if you can get the AA out, you might as well as it'll save the hassle. Having said that, the AA won't come out for it a second time, so you'll either need to drive it yourself or get them to drop it off at a garage for you.
I've done both the engine & box up and out and subframe down one side method. I think the latter is easier and sometimes (depending on engine and box, you don't need to completely drop the offside of the subframe.