Im sure there are adapters out there, but all the ones I have ever seen have been for running a 1x pci-e card on a pci slot. Trying to run something with a pci-e x 16 on it, havent seen that. Could you theoretically daisy-chain a pci to a pci-e 1x and then 16x to 1x riser to go into that? All the connections would line up, but would it actually run and be seen by Windows, thats a complete other matter.
ya i was thinking about that