I've mixed oil and grease for decades to come up with the viscosity I considered ideal for various applications, but never have I heated it, because you don't need to.
Fashion up a stirrer, whether it be something fancy or just a piece of wire bent in a few hoop shapes like a kitchen wisk, then just put that in a drill, or easier still a drill press.
You can go further. You can also, or instead, mix in gasoline to make a viscosity you can pump into areas where you need it to flow into crevaces, but want the gas to evaporate and leave behind a higher viscosity. This is particularly useful for relubing mechanisms with old hardened grease in place, where it is not reasonable (or necessary or worth the bother, etc) to remove and clean the entire mechanism when it just needs infused with some gas to loosen up the old grease, then new w/tiny amount of oil added. The alternative for those who don't want to bother is just flood the area with WD-40, move the mechanism around, then add the grease while the WD-40 still has the old grease softened. To clarify, a significant gas addition is something you do for an automobile you can store outside till the smell goes away, not indoor applications. Indoors, use the WD-40 instead.
Now here's a crazy question. If 5W30 was only a "little" light, why not just use a heavier oil like gear oil? There is a range of viscosities from oil at room temperature to grease at colder or room temp, or warmer, and you can get whatever you need, as a ready made product. However I don't like to stock that many goops as ready made products and take up the shelf space and tie up money unnecessarily for 5X lifetime supply of something, many times I only need a few drops per decade of something so no way I'm going to buy a tube just for that. Instead when I mix up up a batch of a certain viscosity, I just store the excess in a plastic pill bottle, or syringe, or syringe w/needle application, or an eyedrops bottle, or... I have a few, lol, but most important to me is they have practically no cost and very minimal storage space needed. I can store 10 goops in the space that one grease cartridge takes up.
As far as taking 5W30 9:1 with (NLGI 2?) grease, that is about the ratio I use to relube substantially worn, motor sleeve bearings. Less worn, I'd just use straight 5W30 or W20 or 0W20.
Shotgun? I don't think this is the right direction to go, that a lightweight oil is better and just apply it more often. What problem are you having with it (not) stay on parts very long?
