That's really great Wayne!
Feeding water into a live boiler is how the real systems in prototype industrial steam do it!
Of course, you have to be a bit careful not to "kill" the boil by pumping in too much all at once, so fewer pumps more often is the way to go .... just like you were doing, and using warm water definitely helps too!
I have locomotives that are fitted with Goodall valves which seem quite "thirsty" at times, so I'm left with one of two choices, either use the squirt bottle pump to add a little every few laps, or plan on pulling into a siding and sitting a while in order to catch the boiler back up to near full, and then wait to bring it all back to a boil.