It does sound most probably like a heat issue - the first things which may make a difference if you haven't tried already are to provide maximum airflow under the laptop while watching (if that's possible) and if your laptop has any controllable CPU scaling, you can experiment with that to see if it helps.
If you only watch DVDs occasionally like on a long trip, it's also possible just to rip it to the hard drive, although this is generally a hassle and doesn't really solve the problem.
Apart from that, I can't think of any simple solution apart from drilling, but at this point it's probably best to stop taking my advice
/ –
