Having just done one full, I am also experimenting with this.

at that race I used a combination of roctane gels I brought and gatorade endurance from on course for both the bike and run. It worked ok I did feel some GI issues on the run but was able to keep it together.

Been trying out infinti during training and really like it. Doing another full in July and I am entertaining the idea of carrying single serve packs of infinti.

In combination with a speedfil bta, mixing the packets with on course water to fulfill my on bike nutrition. Any body have experience with doing something similar? Haven't tried such a thing but theoretically it seems easy enough and a conservative plan.