payment options based on category - possible?

[jonias]

I'll preface this question with the fact that I'm not dead set on the best approach to this so I'd appreciate any ideas.
The problem:
My client has two main "types" of products. One is standard pay and ship, the other is a subscription based product which ships new at the first of the month which would require manual offline processing (or would it?).
The solution?:
What I would like (zen) to be able to do is, detect if a product from categoryX is in the cart and if so, only present the customer with the offline processing option.
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If this is a possibility or if you have any alternatives I would greatly appreciate it.
If you're a developer who can assist me with such a mod I would be glad to discuss this with you.