That reservoir used to be prone to develop cracks. I'd reconsider it.
As for the mod: you won't benefit from even more than 1gpm, probably. Is your ST30 the highest component of the loop? You could use the alternate ports as fill ports.
Another way to set it up would be a Y fitting in the top of the reservoir. One input would be the return line, and the other a hose coming down from a fillport.