If you search the forum for 'merge projects' you will see a number of discussions and possible ways to do this at the C2 project level. Usually the answer is 'not easily'.
Few questions though..
1 How big are the projects? (objects/layouts/event sheets)
2. Do they each have a similar structure, e.g., a "MainMenu" layout/event sheet, "SaveGame" layout etc?
3. Do they share some object names, e.g. "TiledBackground", "Player", etc?