2006 Cobalt SS 4t45e - hidden manual first gear?

I have the drive train out of a 2006 Cobalt SS 2.4L that I am putting in a rock buggy. As I was tearing my donor Cobalt down I noticed that the shifter had 6 positions on it:

P
R
N
D
I = automatic selection of gears up to 3rd gear.
L = automatic selection of gears up to 2nd gear. Or in other words, L gives you first gear until the computer decides you need 2nd and then shifts for you. There is no way to hold the trans in 1st gear against the computer's will.

However, once I had it torn down I noticed that the transmission and Range sensor themselves have a 7th position beyond the shifter's L position. I assume this is the first gear position which you are hardware-locked out of using the factory shifter.

I have a buddy who is using this same drive train in a buggy similar to what I am building and I talked to him about this. He wasn't able to keep a manual 1st in the L shifter position. He can shift to L and get first only until the computer decides to give him 2nd. Once I told him about the 7th position he disconnected his shift cable to see if he could put it in the 7th position and get manual 1st gear. While he could get the shift rod on the trans into the 7th position, unfortunately the computer still wouldn't let him have manual 1st. The car acted exactly as if it was in L, giving him 1st for a brief period and then going to 2nd. So obviously the computer is preventing a manual 1st gear in both the L shifter position and the "hidden" 7th position. I hypothesize that simply disconnecting the range sensor might give him a manual 1st in the 7th position but he hasn't had time to play with that yet. I don't think this would be a long-term solution even if it worked though.

So my question is this: Does anyone know exactly where in the transmission tune you would modify to make the computer allow you to lock it into 1st gear?

I've attached my tune which is similar to my buddy's.

Attachment 53940

I know this is really old but does anyone know if this can be selected from the shifter with some work? I need 4 ranges to do this and don't want to put in a different shifter.

Attachment 71689

looks like all signal options are taken already.
first and third are your single solenoid gears and 4th is your dual pack gear. without another solenoid to give you a fourth solenoid engagement option you wont get 2nd to enable.

Finished the engine a few weeks back and will get back to this. How quickly you can spend 7K on a robust street / track engine.
I may not have been clear in my first post. My schematic is doable as others have done this with switches... wall switches in fact. What I was really asking is: what is necessary to get the shifter and trans down one more selection? I may have to make a shifter movement without an actual cable movement.
Attachment 83032
Attachment 83033
Attachment 83034
Attachment 83035
Attachment 83036