Here's an idea to bounce around. DynapowerUSA makes these TurboBox external PCIe enclosures, and one of their models, the NA211A, has a self-contained 220W power supply and a double-sized slot space for potentially a graphics card. These enclosures have the option of interfacing with a laptop over ExpressCard34 (!), or a desktop with a provided expansion card. At that wattage, might you theoretically drop a 6970 into this, or maybe a 6950 if you wanted to be safe? I really wonder if one of these would work to just plug into a laptop and mine with, or expand a desktop that is already at capacity or doesn't have a powerful enough power supply to add any more cards.
Here's the product page:
http://www.dynapowerusa.com/dyna/ASP/CP_i_NA211A.aspThe problem seems to be their price point, though:
http://www.mypccase.com/pcexbox.htmlIf these were a few hundred bucks cheaper they'd arguably be worth it, for the convenience of being able to use it with an older system you already own, and for the fact that it's self-contained. It might even save you power costs long term versus a full-blown rig if you could run it connected to a more power-conserving laptop over ExpressCard.
For more powerful options, they also make these (but they are prohibitively expensive, as per the same price listing above):
http://www.dynapowerusa.com/dyna/ASP/CP_i_NA250A.aspNA250A-GPU
Desktop PCI-Express Expansion Enclosure, 1000W Single Power Supply with extra 8* PCIe connectors (6+2 pin) for up to 4 double width GPU cards
NA250A-PRO
Desktop PCI-Express Expansion Enclosure, 400W Single Power Supply for PCI-Express Add-on cards w/o requirement for extra power connector
On a similar note, it also looks like it might be possible to build yourself one of these from parts for much cheaper than any of the above by purchasing from the following people (they have the peripheral cards, the host cards, and enclosures, and you would need to add a power supply and I guess some sort of fan):
http://www.arstech.com/item-XPRS-PCI-Express-x16-peripheral-card-xprs_px_x16.htmlhttp://www.arstech.com/item-XPRS-Host-card-ExpressCard-Notebook-xprs_host_ec.htmlhttp://www.arstech.com/item-Enclosure-for-3-ISA-PCI-cards-isax3b1.html