few things here. I would make an evar like:
First watched video
Under allocation:
Original Value (First)
The make it last at last 30 days(or whatever you deem is ideal)
Then I assume you have video events like video views etc. just correlate them against First watched video evar. You can then even go so far as to see what videos users then watched/played after the first to get ideas of longer tail impact. Its session based so will not then fire moer than once unless a new PC is used to access or cookies deleted.
GLTU