You'd be wrong there, Eric. I'd always do it with the EBB mounted in the frame.
I've done quite a bit of B/B changing on our three ravens. Sometimes just to fit longer axles (I use bashguards on the outer chainring position and customised chainrings on the middle, meaning a longer B/B axle is needed to get a good/ perfect chainline) The wife's solo was supplied without B/B fitted because I used some 165mm XT cranks I already had and so didn't buy the bike with cranks. I put a new rear B/B in the tandem just before our LeJog a few weeks back because I thought I'd noticed a bit of grittiness in the feel of it and didn't want it to give us trouble away from home.
Anyway, if you make sure the clamp screws are properly tight (I just use a standard ring spanner on them and don't put silly amounts of pressure on it), you can easily put a 1/2" drive torque wrench on your B/B installation tool and put 70NM (Shimano recommended torque) into the B/B without the EBB slipping. In fact I didn't twig at first that my cheapie torque wrench only works on right hand threads and the the non-drive side is a left hand thread. So I put way more than that into the lock ring side, trying to get a click which wasn't going to come. Luckily the XT B/B's use an alloy ring rather than plastic otherwise I'd probably have stripped it. But the EBB didn't slip.
One thing I would suggest is that if you think there's a chance of the installation tool falling out of the bottom bracket as you try and put the final bit of pressure on it(which is quite possible as the spline thingys are really quite shallow), put a soft headed quick clamp or similar across the axle and wrench to hold it in. You don't want the tool to slip because you could easily damage your paint if it does.
