Pushups have always been my week point on the PRT. For over a year I had been doing the once-a-day workouts (several sets of so many, pyramids, etc) and it just never got me very far. I'd be doign sets of 30, 35 on a good day (note: thats for 4-5 sets, my PRT scores were around 45).
I started doing the Armstrong Pullup workout (ask any marine, or google for it.
www.texasmarineofficer.com/armstrong.html i think an address for it). Part of it is starting your day with 3 max effort sets, about 5 minutes between sets. When they say max effort, go until you need to use your tongue to drag yourself to the shower, not until you feel really sore. Then theres the actual pullup workout later in the day (can be done in less than half an hour).
Since I also work an office job 9-5, I try to slip off to the back room every once in a while and just pound out a quick set. Usually I can't get in more than 3 or 4 sets during the day, but it's better than nothing, and after a week of that your arms are so consistently sore that it doesnt bug you to keep pushing for those last few reps.