The platform would have to eat the loss, much like central banks do when they try to maintain a peg. 

 They should not be selling SBD, only buying (I don't consider the distribution of SBD selling). And they should buy at $1, and $1 only, no matter what the external price is. That way the SBD maintains the minimum value it was intended to do, without the need for the more exhaustive monetary policy required to maintain a hard peg.