Also I am not sure if you can take someones else .app file and sign it with your provisioning file.
On a second thought I am sure you cant.
Because the App id has to match the certificate which you get from the developers site (to which you have access only if you pay $100/yr)
I'm an iOS Developer. Long ago (about 3 years) I published an app on Cydia. If I remember correctly, the process at that time involved re-signing the app binary, so I actually think this may be possible.
Publishing on the App Store is indeed the most promising route. I'm not sure I want to risk submitting on my account, though, as I have other successful apps published under that account. Maybe we can establish a new Bitcoin company for the sole purpose of trying to get a Bitcoin app published on the App Store. If anyone's interested in helping with this, contact me.