Make sure to print a small tutorial on the back of paper wallets on how they can transfer these coins to their wallets which they should make.
Also, keep back up of the paper wallets with you and in about 6 months time, check if any of the coins are unclaimed, then you can have them back for you don't want them to go to waste. Or keep track of which key was given to whom and maybe contact them again to ask them why they didn't use their bitcoins.
^^ i was thinking about this to... If you force them to download a wallet on their smartphone, and transfer funds directly to them, i guess at least 25-30% of them will never touch the app again. In 6 months time, at least halve of those apps will be removed from their phones, and those coins will be lost forever.
If you print out paper wallets, it'll take more effort from the receiver. He'll only install the app + sweep the paper wallet at home when he's really interested, so maybe the ammount of coins being lost is not that high.
Print a clear TOS at the back of the paper wallet, indicate that any unclaimed funds will be swept onto your own wallet again after 3 months... that way you'll have some more funds to give away at your next demonstration