I want to make a retro computer around a 6809E and a CPLD. It occurs to me that the physical layout/design of this board would be nearly identical for all the 40 pin, 8 bit CPUs except for power and ground. I want to use a Lattice ispMACH 4000ZE for the CPLD (3.3V I/O, 5V tolerant) and primarily I'm interested in the Z80, 6502, and the 6809E. I'm not opposed to supporting other 5V, 40 pin DIP CPUs.

As an example I know that PROM programmers implement software selectable power and ground pins.

My experience is mostly software and digital logic. I suspect that this can be fairly easily implemented with some sort of pull up/pull down transistor circuit, but I don't know enough to find an explanation / example.

Thank you in advance!

EDIT:
Additional info that may be useful.

 * The CPLD supports 3.3V LVTTL levels with 5V tolerant inputs so I don't need to level shift signals between the CPU and the CPLD.
 * I'm planning on using a PC ATX power supply, so I have +3.3, +5, +12 and -12 easily available
 * I know I could use jumpers to accomplish this, The reason I'm looking at doing this electronically as opposed to physically is that there are a limited number of pins that I need to support (5 power, 4 ground). I'm not looking at having a completely generic solution.

 * The list of CPUs I look at:
   * Motorola 6800
   * Motorola 6809/6809E
   * Hitachi 6309/6309E
   * Zilog Z80
   * Mostek 6809
   * Mostek 65816
   * Intel 8085