How about this, we put him in on his 300 PL ( being generous ), make it a console command to switch to him, every mod needs easter eggs, raditz, mr. satan, some of the other nameks, perhaps some random humans, and a bunch of other insignificant people in, all as console commands, so no newbs would choose them and think it was totally unbalanced. Mr. satan wouldn't be able to fly or do ki attacks, his one special power would be to make goku's spirit bomb twice as strong. raditz would be 1 hit by any gohan, humans 1 hit by anything except similarly weak people, the namekians can have some ki attack that they can pool together, so if you get alot of em... or maybe just make em all do stuff to help teammates, perhaps dende's healing powers, elder kai can raise power levels (only once, insignificant amount just to keep things balanced.) I can think up a large number of things that weak characters can do to actually aid their team.