Ask a Tech-Priest
The current Stormtrooper weapon that they are phasing in they call a hotshot lasgun Wern, at least that's what it said on the case when I took it from that armory world, but I get what you're saying. My hotshot charge packs from the long las I used in the guard were one shot, so I do understand the mechanics of that. But simply put I am an Inquisitor, thus I can get around that whole needs to be visible thing. But If you don't think it's doable with considerable annoyance perhaps another idea.

Protip: the case is wrong, and was probably given that nickname by some idiot in the Departmento Munitorum who doesn’t know a peak-discharge capacitor from his own elbow.

I’m not saying that I can’t make a weapon that bypasses much of the thermal bloom limitation.  What I’m telling you is that it’s going to take both a considerable amount of time and resources not only to conduct the research itself, but to keep the rest of the Adeptus Mechanicus from finding out about it.  You know as well as I do that the Inquisition and the Cult of Mars are not exactly on the best of speaking terms, and this is exactly the sort of thing they’d love to be able to hold over your head.

Now then, if you’re still willing to commit the resources, I’m willing to commit the time.

If my theory pans out, I believe that I should be able to create a weapon which achieves three main goals:

• The weapon must carry laser energy to its target more efficiently, resulting in improved damage and armor penetration.

• The weapon must utilize all standard Departmento Munitorum charge packs, for ease of reloading.

• The weapon must be as portable as possible; I am aiming to create something which is comparable in size to a lasgun or longlas.