[Kevin]

I've not heard of any hacks for this feature, would be nice but all I've heard of for the SG are add-ons like DCCD, front and rear diff lock kits and 4WD on-demand: 4WD On Demand From 4EAT

 

[Kevin]

Ive read that putting the gear selector in 1 or 2 causes the center differential to effectively lock on demand.

Yes, but at 75% throttle

 

[Kevin]

Yes, which is why the 4WD on Demand mod was created as per the previous link