Dallas North Aquarium and many other aquarium-focused stores offer services, but it probably isn't cheap. I've heard $1/gallon but I don't know what it is for sure. For shorter trips, I've heard suggestions that you can pre-portion dry fertilizers into cups, but that likely wouldn't work for 2 months. The best thing probably is to find a local enthusiast and hire them to do it. Have you attended club meetings? I would start there for sure. It seems like there are some others in your area which would make the most sense.
Michael
Michael