As Dave mentioned, no software program can send signals out of pins 10-13 as the hardware of the port simply doesn't support this. However, you have a couple of options, neither of which requires building your own cable:
1) Presumably you are using a straight-through parallel port cable, which maps each pin directly to its counterpart on the other side. Instead, you need a "LapLink" or "InterLink" parallel port cable, which maps pins 3-6 of the data register on the PC to pins 10-13 of the status register on the amp). Here's a pin-out diagram for a LapLink cable.
As you can see from the diagram, 4 bits can be sent and received using this scheme - specifically bits 1-4 make up the signal, whereas bits 0, 5-7 are ignored. Given the ignored bits, "11111111" and "00011110" are the same value as far as BioPac is concerned, but "00011010" and "00010110" are different values. The highest value you can send is "00011110", which equals 16.
If Biopac only registers input on its status port, I'd be surprised if they didn't include such a cable, but if not, you can easily find them online or at places like RadioShack.
2) Just about every modern parallel ports allow the data register (pins 2-9) to both read and write data. I'd be surprised if there wasn't a way to switch the BioPac data register into read mode, in which case you could use a straight through cable and send 8-bit signals to BioPac's pins 2-9. Possibly you've already pursued this with BioPac support resources, but if not, it might be worth a try.
Hope this helps,