Yes, you can extend him without mortgaging the future, but it all comes down to what decisions you want to make. I think Jared Allen at this point is more durable than DeMarcus Ware. I'd rather keep Allen than Ware at this point.
I think the combination of the two would help out this defense this year, and help you towards making a decision next year of just what to do about certain players.
At a 3rd rounder, I absolutely do it. We have to draft 2-3 defensive linemen next year pretty early anyways. If we can get Allen for maybe 3-4 years... It would be worth it.
People put draft picks on pedestals. Would you trade Crawford for Allen? Cause that is how I look at things. Yeah you can get a cheap young player in the draft, but you can also miss pretty badly. Picks aren't sacrosanct like many would have you believe.