There are quite a few different standoffs available including DA, SMB, Horizon / Evolution, etc. just to mention a few. You can even make them yourself. Companies such as McMaster Carr sell threaded or just center drilled spacers that can be used as standoffs for our applications. You could also consider moving the firewall back the necessary inch which I have done on several occasions. You have quite a few options to resolve the problem.

Also, what plane are you working on. If one of the YAKs or other round cowl planes, having the prop a bit out front is really no problem. Of course on something like a Extra or Edge, that is not really an option.