Could this idea work?

I have a throw away Adwords account, and a bunch of fanpages/external fanpage/app pages which need traffic and invites. Now since nearly 85-90% of users at a pc are facebook users, would it be possible to use google trends and bid on keywords which have little to no competition to send cheap traffic? Anyone try anything like that? sounds like it could work.

Adwords engine looks at destination URL for relevancy to the keywords you are bidding on. You will likely see high minimum bids. Also your traffic wouldn't be targeted, so your action rate will be super low.

if you mean bidding on relevant keywords then sure why not...but your bids will be higher if you have a low QS because of relevancy problems. Basically make sure the sites match your keywords in every way and aren't just some 1 page splash landers.

The hard part is finding a low compeition keyword and having it related to your site while still having your visitors attention.

yeah I think can work

It will be hard to get your visitors to do what you want them to. If you buy 100 people at ten cents and only one signs up it cost you ten bucks for a signup. If you buy one superbly targeted visitor for a dollar you can realistically get several signups for that same ten bucks.