I talked with the guys on the forums. They gave instruction on how to do the install until the people at Mint Linux are able to get their distro add to the project. Also remember this is still beta, so backup before you try!
1. to provide a metalink file pointing to the alternate iso
2. edit wubi/src/inspector/IsoList.ini and add an entry
3. add the entry to the listbox in wubi/src/pages/main.ini
Feel free to re-brand but don't forget to do a bit of publicity for us.