You could try rolling off from about 5000 and up a little, not too much, notching a bit at 1000 and 2000 (or thereabouts, if it interferes with the guitar) and then running an harmonic eq like this one:
http://www.voxengo.com/product/overtonegeq/I don't have any specific tips on that, just play around with it.
The concept is a lot cooler if you manage to make it all on your phone, though.
How about we all pool together and get echo a mic accessory for his phone? Nothing crazy, just something that brings the quality up a notch?
This one:
http://www.ikmultimedia.com/products/irigmiccast/30€,
I pledge 5€.
No excuses! I am so very poor right now, so you all should be able to spit in at least a couple of €'s