Pwn your phone (obviously), and install ldid either via Cydia or (easier) ssh in and apt-get install ldid. then
Just compile the app for Device: Release in Xcode (I'm assuming you're using XCode, since you're in the Official SDK section), go into the Device-release directory, find the .app, SCP it over to /Applications/ on the iPhone, fix up the permissions, cd into the .app directory, and run ldid -S <binary> (where <binary> is the name of the app). This will fakesign the application to allow it to run on pwned 2.0.
Then killall -HUP SpringBoard and you're set!
Is there no automated process for this? Doing this every single time you need to test the app is just not possible for developers. It makes development time waayyy too prolonged.