First let me say, I have not tried the following myself yet, but should work.
I think you can wait till you have a problem, then login to the directv website, and activate the protection plan, then get the problem solved, then after a time, cancel it.
Drawbacks could include (if any) that it would take a tad longer to get the issue fixed via the plan (as it wouldn't be prudent to activate the plan then call the same day with a problem, it would be wiser to wait at least one billing cycle to pass first (they may even mandate it) then report the issue).
It would also probably be fair and prudent to also allow the plan to remain for a billing cycle or two even after the issue is resolved, this will insure that if the issue comes back after a week or so, the plan is still in effect, and your customer log isn't suspicious looking, and like the other poster above stated, it's only 8 bucks.
They may not let you cancel it that soon, like I said I have not yet tried this, if you do try it, let us/me all know how it went.