Personally, I use burner inserters to fuel boilers. They just steal a tiny amount of fuel as they feed boilers, and similarly, can never go offline as long as the supply of fuel continues.
As for other methods of storage, I'm the wrong person to ask, anything that strays from default game behaviour is scripting, and anything that does that with an entity means keeping track of all entities of that type in existence yourself in the script, which is laggy.
Since there were other mods at the time that did scripting based things like that, and they WERE laggy, Bob's mods made a promise to never do that. All bob's mods that do use scripts are usually user activated scripts, something that requires the player to press a button. The only exception to that is the clock, and it has been optimised so many times... it's effectively been re-written at least 3 times.
There are actually other ideas of storing power out there, many people just put a storage tank between the boilers and steam engines and store the steam, so if you ever run low on fuel, it just uses stored steam. Actually, since a nuclear reactor doesn't turn off once you put fuel in, this is an almost essential thing to do if you want fuel efficiency. You basically wire up a system where you only put a fuel cell in if the other inserter is pulling one out, but also only pull one out, if the steam in the storage tank is lower than a certain level.
The other thing to consider though, is I'm not good with graphics, most custom graphics in this mod are done by other people. Adding something that would require graphics is unlikely to get them. I've made several new things for my mods that haven't been released yet because I don't have the graphics.
