That's very neat, thanks. I suggest we write this up on the wiki somewhere so it isn't lost. Chris Raggio was wanting to develop NFC-based "tip jars". Stefan and I brainstormed some protocols for this at the airport on the way back from the London conference but didn't come up with anything as neat as this.

Do you plan to implement it? The biggest challenge I see is scalability. Your algorithm requires running the computation for every input in order to find payments. That is a lot of EC math. I am skeptical it would be pleasant to receive such payments on a smartphone. It'd probably be OK on a desktop/laptop at current traffic levels with a good parallel implementation on an SPV client. I suppose you could have a semi-trusted third party identify the transactions for you (eg, a node).

If you want to integrate your scheme with bitcoinj I am happy to advise and do code review.