You could use the Dremmel, on a slow speed, with the circular saw attachement, but you'd need to be very careful; a razor saw would be better if you can get one.
The reason I mentioned this kit as a good one to 'try' scratch-building, is for exactly the reason you would like to portray the finished model. With the doors open, it would look great with the bomb cart. I think you COULD do it, as it's a straightforward cutting job. Even if you didn't attempt the framework/ribs on the inside of the doors, once painted, they'd be passable. The kit parts alone are good enough to serve as the bomb bay interior, as not much can be seen, unless you turn the model upside down, and use a torch to look inside! (Incidentally, the reason the bay parts are included, is that this kit was also originally issued with one half of the fuselage in clear plastic, so that the interior could be seen).
I personally think that you'd be able to do it without problems, as you seem to have the 'right approach' to planning ahead and improving your skills; this little exercise would give you much more confidence to attempt further, albeit small, detailing work, and the sense of achievement you'd feel afterwards would be enormous, adding to your confidence and, of course, your experience. If you look closely at the fuselage halves, you'll notice that the bomb bay door joints are well defined, and therefore provide a good guide to making the cuts required to separate them. If you do decide to tackle this, leave off the doors until the model is finished and painted, then fix them in position. You can mask the open bay before spraying the Alclad, the job of which is going to be much more complex than attempting the bomb bay job!
This time, I AM going to bed!!
Terry.