There is. Once cargo clears sensor range it despawns. This means, if you go 7km from where you dropped the cargo, you're safe if the pirate wants the cargo.
I've said it before and I'll say it again, the best way to deal with a pirate is to dump cargo and run. Don't attempt to run then change your mind, don't sit there waiting for him to scan you allowing him to get close. As soon as the interdiction closes, boost away and dump what you think will be enough to cause him not to chase you. Then run like crazy. If the bribe isn't good enough he'll chase you, and maybe now is the time to submit to scans and put your life in his hands. If the bribe is good enough, he can't both take the money and you. To minimise risk, make sure it's good enough. Of course, this isn't flawless, as you may have got away anyway with all your cargo, and it's hard to be clear what "good enough" is. I generally work on "if you have no shields, you pay more" and "the more work you make me do, the more you pay". I ask for more from people who run then people who cut engines and let me scan.
Part of the problem is that there are quite a few people who don't care about profits from pirating as they can make 5x more in the same time trading. There are others who aren't really there for the piracy, but to shoot up people who can't shoot back. The above tactic may not work on them.