I think this is a bit one-sided, that you've created "forced buy in". You've also created a LOT of supply as well, which goes a long way to counter-balance the demand.
Besides, the exchanges do not seem to have implemented this as a demerger spin-off (you were short BTC, but you do not need to return BCH - just bTC), and as a consequence NOT created "forced buy in".
Except that you haven't created a lot of supply, because people may not be able to sell theirs and if the coin's useless it may not be worth it even if they can. For example, I don't think either of the major exchanges offering shorts (Bitfinex and Kraken) are accepting BCH deposits yet, and they certainly weren't initially after the fork. Even if they were there isn't enough mining power on the chain to make transfers possible in a reasonable amount of time at the current difficulty. So any shorts could only be closed by buying BCH already on the exchanges, which only existed in the same number as there were BTC on the exchange at the time of the fork. This small supply drove up BCH prices squeezing short sellers. There's also been quite a lot of price divergence between exchanges because people can't transfer their BCH between exchanges.
It is significantly harder and more expensive to do those off-chain transfers in practice.
I should know: I'm actively trying to sell BCH right now with just that kind of mechanism. What would have otherwise been a few clicks on a screen is proving to be hours worth of back-and-forth, and that's for a relatively small deal with a large degree of trust on both sides.
