Umm... So for 2 reels, just put in twice as much. Again, I just don't get what that has to do with dilution, unless he's making it real weak and there isn't enough room. Is that the case here? I've never used HC-110, is 1:49 weak?
1 + 49 is only weak if there isn't enough room to fit enough of it into the tank.
As Gerald says, many people find that they get good results with as little as 250 ml of 1 + 49 HC-110 per roll in the tank.
I just prefer to rely on the no doubt highly conservative recommendations of Kodak and try to ensure at least 300 ml of the stuff is there per roll.
Some have the opposite problem - they have different tanks and in order to economize they try to limit the amount of developer to the minimum amount (250 ml or 300 ml) required to ensure sufficient capacity per roll. As a result, they end up failing to actually cover all the film.
I am not likely to suffer from that problem, because I use replenished HC-110, and allow my tank size to dictate how much developer I use.