You don't, just race

Several years ago I used Mark Allen Online for my IM training which follows the MAF method. If I remember correctly the race strategy was to keep the HR at or below MAF level for the bike and the first 18-20 miles of the run. Then, if your're feeling good, let it rip for the end of the run.

I only did a few 70.3's using the method by my recollection was to do the bike and first 8-10 miles of the run at 5-10 beats above MAF. Once you get to the end of the run, let it rip.

Endurance Planet is the best source for anything MAF related. Offhand I was a couple BPM over MAF on my 70.3 bike didn't bonk on the run but was definitely hurting. Unfortunately I sweat like a greased monkey and my HRM stopped working during the run. During my ironman I couldn't even get the HRM to give an accurate reading throughout the entire race. I know Phil says on IM bike to keep it just below MAF and essentially said to ignore it on the run.