Kusojiji,
Actually the problem is that in a tower type configuration the AGP card is upside-down compared to PCI and ISA cards. This makes all the heat sinks and fans work AGAINST gravity.
Heat travels up, so it soaks through the GPU and the IC board. It has NOTHING to do with RAM. Most RAM, excluding the GeForce FX cards do not get that hot.
The main problem in this configuration is "Heat Soak" through the card.
There are compounds that will allow a heat sink to be attached without shorting out the surface mount components on the back. You should be able to machine a heatsink to mount to the central area on the back of the GPU without touching the surface mount area. It would be a small contact area, but at least it would take the heat off the card.
My two cents...
