Its very simple, make it so that while its buy phase your satchel can only explode if you recast it. If you don't recast it you can pick it up with f like cypher's cage and killjoy's nanoswarm. If the round starts and you didn't pick it up...

I understand the marketing behind the store being 4 randomly selected items, I'm not gonna argue that point at all. What I am thinking of, though, is that this Reaver Vandal in my store that I desperately want but am unable to purchase at...