Since posting this I've had a another go at something I've attempted before, and its been more successful.
I've create a new sketch with a series of construction lines, with co-linear relations to the axes of the holes.
These are then used as the basis for a series of Reference Axes, which are then used for a concentric mate.
Then use intersection to create a series of points on the surface of the belt, one on each reference axis.
These are used for coincident mates on the underside of the mounting block.
The only 2 issues I've seen so far are:
Original pair of holes must be on a flat surface - Not really a problem
The points can occasionally jump to the 'return' side of the belt
If your belt is created with a sketch that is a closed loop, you can use a Path mate to keep the part on the surface of the belt. You would need to go into the path sketch and use the Make Path command to join all of the sketch segments. Keeping the block tangent might be a trick, but if you don't mind a little interference between parts, you can mate the forward edge of the block to the same path. Once you have one block mated in place you can use a curve driven pattern in the assembly to pattern the parts. There is a function in the pattern dialog that allows you to rotate the parts in the pattern to remain tangent to the path.
You might also be able to use the Cam mate in the Mechanical mates section, but I've never used it, so I'm not sure how it works.