I don't know this for a fact, but I suspect weight may also not be useful in this case. I've seen where other blind-boxed items in the past have contained weights in some boxes that served no purpose other than to make it more difficult to determine what's in the box by weight. Lighter items would get more weights, such that each box would have essentially the same weight regardless of which figure was inside.Hunh. Usually blind boxes have SOMEthing on them to indicate... I know I did that for the megablox halo stuff back when...
Well... if it's actually completely random (other than weight, which is what my google searching suggests.)... then I get them from imaginaire and save the money.
Blokees don't have weights in them exactly, but I have noticed that some boxes will have desiccant packages in them of varying sizes. The apparent randomness of it makes me suspect they're a mechanism to prevent determining what's in the box based on the weight. They might be similarly intended to homogenize the box weights, but I suspect they are truly randomized as to what boxes get a package and what size it is so that there's no standard weight for any particular figure.
I go back to the fact that the eBay sellers who sell a ton of these by figure are opening the boxes. If there were any trick to figuring it out without opening them, I'd bet they'd figure it out and use that as an excuse to demand higher prices.