Yea, that would also be a valid option, though if you want the easy soldering option, you would also have to get the big style microchip, and you still have to find a way to hold it all together, and it's getting a lot bigger. On the other hand I'm probably overestimating my own soldering skills too, the smallest thing I've ever soldered is a ps2 chip years ago.
As for making a separate bluetooth one, that sounds even harder to me, and more hassle getting batteries and chargers and stuff. Also it means that you would have to hold your phone and bluetooth box in alignment or it would be completely meaningless.
Since I've been assured that it will be possible to force the usb into host mode, that would be my choice of interface/attachment.