My approach is sort of like Ty's in reply #3, just a bit more complicated.
Figuring the fuse centerline in level flight is just about the mid-point between inside and outside 'g' roll load variations, I 'static balance' the model about the centerline. full weight of lines, reel and clips, etc. halfway from centerline to leadouts equals half the weight at full distance. ( (The flyer carries the other half of line weight in level flight). Brett and Howard both advise this isn't accurate - too many other conditions. I agree, but it seems a reasonable start point. Final trimming always follows in-flight flight observation. (At my 'humble' level, it's good enough) ...And there's no need to weigh anything.
How to do it? With he model upside down on a cushioned flat surface. Place the reel, with flying lines and clips on it, on the inboard panel halfway from centerline to the leadouts. Balance the reel and clips weight with an empty identical reel plus clips the same distance out on the outboard panel. Add tipweight until 'balanced'. I put BBs in the weight box to find an approximate match.
This works well! For one very light profile, it actually found how much INBOARD tipweight it needed!