When you broadcast to enable, it publishes the ip and ports that are open(see ex: https://hiveblocks.com/tx/14e6c348ced9d4211ce8392bf413ba290c754bb2). I guess if you manually broadcast the enable trx(I was told you could do it at https://tribaldex.com/witnesses) and you have a setup that forwards the requests to the proper ports on your engine witness I guess it could work. I'm not really too good with networking stuff though so maybe try it out on an ip you don't care about. I can give it a try this weekend to see how it goes.