I wouldn't worry too much about what they do once they get home. I think most people want to frame the little ones themselves and are just happy to have a 'bargain'. But it's also nice to give them some ideas.
If they are standard frame sizes it's no problem for them to insert them into a ready-made frame.
They can also do the velro idea with a ready-made frame. There is usually a stiff backing which they can cover and then artfully press the painting into place. For a more permanent display they could add a couple more pieces of velcro.
You might want to pick up a couple of little easels and have them sitting on those, making the pieces nice on a mantel or table top. I know they are available here. You might check places that have plate displays.... something like this: http://organizeit.com/poblkplate.asp?recID=3498
If you have one or two of those available or can tell people where to buy them, that gives your client another display solution for the smaller pieces... If you have those little easels available, you could just charge the actual cost in order to get your money back.