This is the first instance of me hearing about someone wanting to MOD their GameCube. I say don't do it for several reasons:
1. It's uncommon. Since most GC owners are happy with the product in the first place.
2. Piracy destroys Nintendo's Revenue, which ultimately cuts into the cost of games and the resources to produce them.
3. You need to buy those smaller DVDs to burn games onto... seems like a lot of work, energy and time to do this.
4. There is already a bookdisc available, so no need to modchip.
Good luck!