Bernie,
It may be possible with some fancy VB work.
The 4L80 is essentially a TH400 with an OD unit added to the front of the main drive.
If you could turn the OD on in each gear, and then back off at the gear change, it would function as a 6 speed.
However getting the shift timing right, so that it didn't hurt parts by having a bind-up, or hurt clutches because of a flair might be tricky.
Very few applications should need such a unit, very close gear spacing. Only a high strung very narrow power range engine would need it.
It might be neat to turn the OD on at the top of 1st, then shift to 2nd, then 3rd.
Or even to have the option of launching with OD on, but go through 1-3 normally, however on the 3rd shift, you would actually be in OD.
Would be good for testing purposes anyway.
I'm sure it could be done, but it would also be harsh on the OD clutches to make 3 gear changes and releases in a short time. That's alot of heat buildup in a short time.