Creating a Loader to modify a DLL file

Well,actually there are a few Methods.
You could go and "hook" the Loadlibrary Call that loads the dll, thus obtaining the dll loadaddress. from that you can walk the export table to get your functions and/or calculate any needed distance values. Another Method would be to use toolhelp/psapi functions. you can locate your main app and get its loaded modules this way. you will also get baseaddress/size whatever and can just read your dll out that way easiely
The "handmade" export forwarding will work too,but i guess its more work to the thing already needed.