Well, I think I found a 'solution': just have to keep my pc somewhat busy, I let it play a movie over and over again during the night and my hashrate stayed at a constant lvl of 78mhash/s and temperature even stayed below normal level, yet it still generated the expected shares as when I would be using my pc.
I'm using an ATI 6650M gpu card on my pc (+/- 80mhash/s and yes I know I'm running at a loss at that hashrate please do NOT comment on that but on my question). If I'm using my pc it's around +/- 80mhash/s, and when I'm not using my pc, the hashrate goes down after 15 mins to about 45-50 mhash/s. I suppose this has to do something with sleeping/idling power settings or something?
Also, mining with cgminer at intensity 3 since it gives me best/most efficiënt hashrate
Any suggestions how I could keep it running @80mhash/s without having to move with my mouse every 15 mins to get it to full speed again?
I suggest you take a look at SBC (Stablecoin), 25SBC/block and low difficulty. You'd obtain them quickly, and able to sell them at exchange (as Cryptsy for SBC) and buy them in for lower price again and so on and on...
Feathercoin (FTC) and Peercoin (PPC) are nice too though...