Here's the idea, it's a little tedious but not difficult. Say you have 200 seeds. Each seed is numbered 1,2,3 etc. Then you also assign a random number to each using http://www.random.org/nform.html. So in this example, you would generate 200 numbers with a value of between 1 and 1000. The computer spits out a unique list, which you can print out or otherwise save. Those numbers are then assigned in order. So a seed might be 1-834 or 2-119,or 178-004. This asks a lot of work on the part of the grower, but for seeds that are reasonably expected to be hot, it could just about eliminate fraud or substitution.