We are thinking of offerering a service with bonding to our customers. Here is the question. Say we are running MT for both AP and client and on the AP side of things we run 2 Radios and on the client side we run either 1 or 2 radios (depending on wheather or not the client wants bonding for extra speed). Is it possible to run bonding in a PtMP environment with either 1 or 2 radios on the client side?

You need 2 radios on each side.
You need to create 2 WDS links (each WDS on different radio).
On each side you should habe bridge or ap-bridge mode.
Then you can create bonding using those 2 WDS interfaces.