As I learned from the issues on this GitHub, you are supposed to be able to modify the rf/t accepted by the Builder via the corresponding config file.
Since I have the required power gen in my world I wanted to increase it in order to mine faster for my resources.
I changed the builderRFPerTick setting to 500k in the rftoolsbuilder-server file and restarted my server but it still only accepts 20k rf/t per side.