If you look at the riser cards that add slots (not just a single slot going horizontal) you'll notice that there's a surface mount chip on the board. Without going into too much detail, some of the PCI signals are slot specific. Meaning, the motherboard associates certain controls lines to specific PCI slots. Each slot is not aware of these other sets of control lines and merely waits for the PCI arbiter chip from the motherboard to allow it to transfer data.
That extra chip on the riser card is a bridge chip that functions as a "pass-through" PCI device and handles all of these control signal issues locally.
So, in other words, you can't just "daisy-chain" multiple cards together from one PCI slot. Not all of the signals will be present... not to mention you would have a hell of a headache dealing with trace length issues, clock delays, impedance mismatches, and more.
The easiest thing is to just buy the riser card and enjoy!