Solid arguments ttl ... -.-
Originally Posted by name='"wikipedia"'
A PCIe card will fit into a slot of its physical size or bigger, but may not fit into a smaller PCIe slot. Some slots use open-ended sockets to permit physically longer cards and will negotiate the best available electrical connection. The number of lanes actually connected to a slot may also be less than the number supported by the physical slot size.
While wiki is not the best source, this suggests it could
be possible, which still doesn't say a thing. From what I understand of it is that it's possible to insert longer cards into shorter slots as long as the rear is open ended like the x4 slot (that's the middle one) on this pic:
Also came across an interesting topic on this while googling:
It seems to work there.
EDIT: there's of course still the possibility of two PCI based cards, which are pretty cheap.