There is a post in this thread that mentioned just adding the spices directly to the secondary for a period of time before bottling and they pretty much picked up no flavoring once bottle conditioned. Not sure how long it would take to get the same effects as the tea when you just add the raw spice to a keg. Could take a long time and you would more than likely get a more prominent ginger flavor over any other, just because the nature of the raw spices I would either make a tincture or tea. the Tea has always come out on top. Vodka like,
@BrewCityBaller is doing, shouldn't impart any flavor and will create a strong tincture. But then you have to do more calculations to get the ratio correct for your addition especially if you are bottling. Not so much for kegging, bottling you would add a few drops to each bottle then add your beer on top.
Cheers,