Building time is all you want? Just hours in a logbook?
Pencil them in. Use a pen if you wish. Falsify, and make them up. Write in whatever you like. It's just about hours, right?
Do not build hours. Build experience. Hours and experience have no correlation.
Two people can fly an hour in an airplane, but one can come away with an hour of time, and the other an hour of experience. Be the one that gains experience.
What you do with that hour is everything, as is what you take from it.
Numerous avenues are available to gain experience without having instructor certification, but why would you not want to instruct? Instructing offers valuable insight into what you do; you learn a lot, and if you're dedicated, you can give a lot, too. You'll find few professionals in the cockpit who don't have instructing in their background, and who don't hold a current instructor certificate. Even if it's hardly been touched in years...most find that keeping the certificate is worth the effort to maintain, and those who don't keep it seldom regret having instructed.
Join Civil Air Patrol. Become a cadet orientation pilot. Become a mission pilot. Get actively involved in search and rescue, and other missions that CAP provides. You'll find that reimbursement for the airplane, or use of corporate (CAP) aircraft reduces your cost to little or nothing, for your flying.
Tow banners. Do traffic watch. Fly skydivers and pack parachutes on the weekends. Take whatever you can, where ever you can, and get as much as you can possibly get from it.
Don't settle for "building hours." If that's all you want, write it in the logbook, and be done. You'll come away with as much as if you'd "built hours" in the airplane, for a lot less headache and hassle. The only reason to go get those hours in the air is if you're after experience...and then you've got something to talk about.