Is this even possible with a combo amp?

I just bought my first all tube combo amp... a nice little 15 watt Ampeg. This amp, like many combos that I looked at, has multiple output jacks in the back so that I can use the combo much like a head and have it run through other cabinets.

However, I was wondering if the opposite is also possible. Since the internal speaker is connected by a simple cable, why couldn't I find a nice little 2-watt head and connect the internal speaker to it? I'd have to extend the little cable since it is short, but length issues notwithstanding, is this something that might damage the amp? Does anyone else out there do this?

Thank you for your time and help!