You could use an external midi processor app like Midibridge (iOS) to translate Pitchbend into filter cutoff. Midibridge would also allow you to create an algorithm for this translation. This would enable the fine tuning of the translated control effect.
This is a good suggestion. But you see where I'm coming from right? For any analog synth, having the option to couple the filter cutoff to the pitch bend, much like when it tracks the keyboard, creates such a great expressive (and natural) effect it seems like a no-brainer to me.
I plug my Linnstrument straight into the Prophet-6. I'm bringing this up because of how well the P6 handles these advanced controllers, for example polyphonic aftertouch.