I saw you somewhere! :D

Unfortunately, no easy way to do that.

You can ask winner to make a screenshot of web page for that DLC (of course, winner should be logged in) or a screenshot of Steam client with game highlighted (it will show the list of already owned DLCs).
Winner can crop out the account name and other personal details.

Or you can give DLC away without checking anything if that's too much work, work both ways :)

forgot I had it and SG doesn't hide it

Ah ,ok ,no prob.

Thanks !