Personally I believe a Code-0 or hooter will only work well with a concave leach (arc-ed towards the luff). As it won't have enough air pressure or draft to keep open a convex leech (prevent leech fluttering).

Oversizing the foot won't help here either as then the 75% girth will become larger as well.

Only thing you can do it oversize the leech and thus shortening the foot and moving the girth measurement to lower in the sail hoping that it will make 75% ofthe (shorter) foot length there. However this will make it a very sensitive sail to sheeting changes.

In my personal opinion trying to make a true code-0 work within the 75% girth rule is a waste of money and time. For good upwind performance it will need to resemble the shape of a jib and that sail has only a 50% girth measurement. The difference between that and 75% is just to much to overcome by some trick.

Of course there is no point in throwing out most of the code-0 benefits (if any) by forcing it to adhere to the 75% rule. Will be much better to just go fully non-compliant and get a proper code-0 or just forget about the whole thing and get a flat cut assymmetric that allows you to reach if not to sail upwind.

It is better to have all of one thing then a bit of nothing of both.

Wouter