I think this is a great idea. Anjay, the exact reasons why you say it won't work are the reasons I think would work.

Here's an example you have a parent that hosts a site with you, they have kids, their kids are really getting into the whole internet thing and they want their own site. You sell them a gift certificate maybe have a discounted price for gift certificates, now the adult is paying for the site, so you don't have to worry about the cash, they started their kids new site with let's say a 10% discount from your normal price, you just sold one client two plans (their original one and the kid's plan).

They already have to be a client of your's to get the discount rates and gift certificates. Selling non-refundable gift certificates that are 10% more than the original amount used to purchase it sounds like a very good idea. What's the worst thing that can happen? You wasted time creating another page on your site, that's about it, the potential benefits definitely outweigh the risk. Being in the webhosting business itself is a risk, and this is a very minimal risk. I say go for it. You might be surprised with the outcome.