How to make a Universal Binary out of two separate projects?

I have got an iPhone and an iPad app - both are separate fully working XCode projects. What I want to do is make a universal binary app out of these two. how can I do it?

Thank开发者_开发百科 you!

If that projects using the same code it would be quite easy: just create new project, add sources and set Targeted device family to iPhone/iPad. However if you have separate code for each device, my congratulations, you'll have a big pain in the butt: you have to merge that sources and check for the device at runtime. Everything else is like in the first case.