I take it the drawer is open? If so, you can just replace the lock with one that has two keys for it.
Depending on what type of lock it is, it can be quite easy.
Is it a cam lock? (with a flat bar that flips up to a slot in the underside of the desk? If so, a pair of channel lock pliers and a phillips screwdriver is all you need to replace it. Homo Depot sells them for $5.95 I think.
Does it lock all the drawers simultaneously or does it just lock itself? Then it might be a straight lock (a single flat bar move up out of the drawer into a slot into the underside of the top).
Is it the centre drawer or one to the side of the leg opening?
Is there one small and one large drawer?