for what its worth, my oppinion is to use a carboard roach. you can make it whatever size you want, so the issue of it fattening out the joint is redundant. there is in fact no reason to not use cardboard except laziness or habit of collecting roaches to smoke later. dont grind it too fine for two reasons: if its too fine, it will burn reallly quick and the joint will be gone in a puff. also, the finer you grind it (past a point that is), the less space it is gonna fill up so your joint will be smaller and smaller. roll it tight. there is absolutely no risk of rolling too tight to not be able ot suck through, with joints this big. the aim to get as little airflow as you can actually, with these little joints. you want it to ONLY burn when you suck the hell out of it, or else all (the tiny amount) of your weed will be wasted. using a filler will make each puff of smoke contain 50% less thc but will not change the amount of thc in the joint, thus it will be profitable: you will lose 50% less thc in idle smoke (which can be half the joint if its small), it will be much, much easier to roll thus this brings all the other benefits of a well rolle djoint over a badly rolled joint and if yo uuse a nice tasting filler, you can make exotic scents waft out of your joint and hang on your breath.