Could two parallel threaded shafts give you what you need? You could use something like a single start acme thread. One will translate motion to the other and there would be no backdriving.
Essentially, I think, what you're asking for is a wheel of infinite diameter to mate with a worm. This is of course possible although, in answer to your question, the "rack" can not be hobbed or fly cut as you would cutting a wheel. Your options are; form milling, gear shaping, wire cutting.