Whenever I do a timelapse, I usually just take a straight video at the lowest fps the camera is capable of, then drop frames from the video until it at my desired length. This means you don't need to do any firmware fiddling, but it does mean you need a big memory card and a power source to keep the camera running.
Tools:
-
Rad Video Tools - Can convert pretty much anything into AVI files
-Virtual dub - Can very quickly drop frames from AVI files
-Xvid codec - A reasonable compression solution
Process:
1) Take video
2) Use Rad Video tools to convert it to AVI, if necessary
2.1) Open tools, find video
2.2) Click "convert a file"
2.3) Choose "AVI" as output format
2.4) When prompted, choose xvid as compression format, choose high quality level (you're not keeping this file, so don't worry about size)
2.5) Save
3) Open AVI in Vdub
3.1) Video->full processing mode
3.2) Video->Decimate By->[enter the ratio you want your video to be faster by)
3.3) Video->compression->xvid (choose a good quality)
3.4) File->save as AVI
3.5) Wait...
3.6) File->open your AVI
3.7) Video->direct stream copy (makes sure it doesn't recompress when you change your frame rate)
3.8) Video->Frame rate->30fps
3.9) File->save as AVI (this will be your final file)
Done!
It seems that not many apps have the ability to directly modify frame rates, so Virtualdub is what I've always used.