David, I have an extended probe on one of my 2240s, one that I fitted a steel breech and shouoder stock to to make a 5ft.lbs mini-carbine.
As you have the facility to make your own, I'd stick with the probe idea as seating pellets with some alternative tool might be tricky due to the tight breech access and, of course, you need to not compromise the sealing aspect. I also wouldn't be wanting to go TOO long on an extended probe as it can make rolling pellets into the breech a much more fiddly affair. Maybe 1.0 to 1.5mm longer, 2.0 max? (Nothing scientific here, by the way). And you could experiment with the profiling of the narrow part of the probe re gas flow? Chrono testing will then, hopefully, highlight what works best, not forgetting to take into account temperature fluctuations.
Hope this helps a tad?