The other reagent for syn dihydroxylation is OsO4.
For both KMnO4 and OsO4 - I am not aware of any endo/exo preference, but in either case it won't be 100/0 so you will get both the endo and the exo - one will be the major product and one will be the minor product.
Will they mind that the product from c will be racemic?