If by a substitute you mean a similar "old style" looking font, then Al Bayan could do though it has a rather poor set of ligatures.
But if, shameless, self-promotion is allowed I'd suggest you check my (freely available) Amiri font which have rather a very rich set of contextual forms and covers almost all Unicode 6.0 Arabic block.

And such a pair would work nicely, "on a more subtle level" then just visual equivalent - if I could add my opinion.

Thanks for the advice.