This type of idea usually happened when going out with friends. More like outing than photo shoot session. You might want to try passing a PnS camera to the model and using the DSLR for yourself. As you go along, you can shoot each other. Although there are models who are photographers themselves, but I don't think any model would like to shoot someone and pose as a model on the same session (I might be wrong).
As a TFCD model, I believe they are more interested in getting acceptable photos so that they can add to their portfolios, you idea is good. However if you ask me (as a TFCD), I'd think wasting my time (I might be wrong again).
No offends, just to speak my mind.
Care to share with us your previous successful case on this? Some photo would be great.
Good luck.