They should stop that. It is silly.
Hmm. Saying "don't have the problem" isn't quite what I'm looking for here. I will edit the OP in case you think I am suggesting making any changes to the network. I am not.
Whatever convoluted workaround we come up with is going to be far worse than simply doing the right thing.
I'm not sure that this is the case at all. Please elaborate if you think this is the case.
The right thing, by the way, is for the casino to request a return address (address A), then generate a new address (address B), and link them in a database so that earnings made with BTC deposited to address B will only be returned to address A.
Anonymous services may not wish to do this. Avoiding suspicion of money laundering is one possible reason this method might be impossible. (This is the stated reason for the casino - it only gos back to where it came from = no money laundered here)
Also, regardless of the seemingly silly issue being directly discussed, can you not think of any reason ever that one person might wish to refuse an incoming transaction from another? I can think of several.