To design JTAG cable using parallel port.
The normal 1284 parallel port printer handshaking signal 5 pins of the port have been use for the 1149.1 signals, TCK, TMS, TDI, TDO and TRST.
Normally, Altera or Xilinx give you the tools to program with circuit to connect to parallel port. Try check the signal on parallel port using for JTAG signal mention above. If they use the same signal, you can modify the connector to be the same. And you can have your own proprietary cable for both mfr.