It seems nobody knows it (not even the so called guru), but you can actually put an overlay link inside a youtube video, I mean a link that points to any web page outside of youtube ! Everybody can do it, not just "youtube partners" .
basically you have to use the new "promoted videos" from youtube.
Start a campaign with adwords using the promoted video, so you choose one of your video you want to promote (see the video below for explanation). .
Then you can pause the campaign right away (so you don't spend a cent): having a "paused" campaign (as long as you want) is enough to have a new opportunity for your video, youtube now gives you a clickable overlay inside the video, you will set it from the edit page of your video (you can see what I mean watching the screencast).
This is the only video that explains how to do it, the screencats is made with the italian interface of adwords but hey ... you can get the overall method anyway.
Of course if you use crappy methods to increase your video views, youtube could eventually turn off the overlay and video itself.
youtube.com/watch?v=MzekSQ0LPsk