Can this be done and what needs to be done to the computer or harness to accomplish such a task?

 

What PCM?
All DBW PCM's do not have IAC drivers in them, if you search you can find a list of them.
You need to change the plugs at the throttlebody, and move some wires at the PCM connector. If you want a cleaner instalation, you can take the wires out going to the TAC module. You will also hace to flash the PCM with a tune from a DBC vehicle. It helps if you give more info on the what drivetrain and PCM you're using

 

I just recently modified a C5 wiring harness (DBW) to work in my conversion with a 4150 style throttle body. For my build I wanted to clean up and hide the wiring and engine bay as much as possible, so I stripped the harness and removed what I didn't need.
Start out by researching and printing out the wiring diagram for the vehicle your harness & ECM came from and also a diagram for a drive by cable vehicle (99 up F-body for example). Remove the wiring that you won't need (emissions, TAC, vehicle specific, transmission, etc) and then go back and add a pigtail for IAC and TPS. I bought those pigtails from a vendor on Ebay.
It can look very intimidating, but just be very methodical about it and don't let it get overwhelming.

All of this mess:


Can be cleaned up and look more like this:

 

The ECU is an E67 that I would like to reflash with a HPT 2 or 3 Bar OS.

The harness is the GM standalone harness.

 

I don't think there are any E67 drive by cable applications, are there?

 

Nevermind, I decided to use an LS2 throttle body that I had laying around and just stay DBW.