A system similar to what you would need for orbital bombardment was developed by the US for espionage satellites. The KH-9 Hexagon carried four film capsules, which would be ejected from the satellite to reenter the atmosphere so the film could be recovered.
Basically you need two things for an orbital bombardment system:
- A heat shield that allows the bomb to survive reentry. This should be well within current technology, we can get (fragile) humans back from space in one piece after all. Ballistic missiles already use heat shield for their warheads, these are rated for the lower reentry speed of an ICBM.
- A trajectory control system that allows reentry in a small target area. Again, the reentry of manned space capsules shows that this is doable.
As others have said, a satellite isn't strictly necessary, you could launch each bomb with reentry vehicle by itself (or deploy a group of them from a single launch).
A final issue is how the fissile material would stand up to space radiation. Would it cause extra decay of the uranium, making the bomb less effective over time?