Electronic upgrades, just like vouchers, can be gifted to anyone you want. According to the program rules, they can't be sold or bartered (same as vouchers). So, if the airline catches you, at the very least it will void the upgrade.

You were very lucky if you sold travel vouchers on eBay and got away with it, since it is well known that airlines monitor eBay (and craigslist) for this sort of transactions.

In the end it's up to you and your risk tolerance, but in this case I'd say the risk greatly outweighs the benefit (since, as I said, not only you risk losing the upgrade, you risk being forced to pay full fare business on the spot or being refused boarding).