i'm not sure how realistic this idea is. the reason i say this is, what happens when you adjust you drag on the river? say you get a real hot fish on and you loosen or tighten the drag down, are you going to pull your scale out while your on the bank to reset your drag after you temporarly adjusted your drag. I just have a funny mental image of someone doing this while other people are fishing....i think you might get some funny looks.
I think it boils down to the couple of tuggs you were talking about. I hope i'm not sounding like an A**hole.
I guess you could try the scale method at home, and then see how it feels while you pull the line out by hand, then you would have an idea what it feels like, and could remember that for when your on the river.