Unfortunately, you will need to replace the sub-frame.
There is another option though, but it is a custom fabrication. Find a set of the plow-head grips and trace them on paper, paying close attention to screw hole location.
Then, with the birdshead grips off your UNLOADED firearm, place the frame over the traced grips centering the screw hole of the firearm over the paper screw hole.
Now trace the birdshead subframe over the tracing of the plow-head grips. This will indicate what material needs to be removed from a pair of walnut blanks of the correct thickness. Then remove the wood only in the birdshead area and the outside of the plow-head area. Constantly checking fitment when getting close to size.
Finally; sand, stain, clear-coat the wood as you like.
I typed this out so that maybe someone here with the skills (or you, yourself) would consider the build.
I see a plus with making a pair of "convertible" grips. You can easily swap back and forth, like owning two guns, and if someone fabricated them, they would have made
a template for future grips... whether or not there would be a market would depend on other owners.
Food for thought...
~
Enbloc
EDIT: A power scroll saw would really shine in this roll, as well as a Dremel...