Most probably it will not be an interface, since you have to manage the following (t least):
- replace high memory with new 64K 4116 chips, that are completely good
- rework some of the internal decoding logic, to support the extra memory
- support some kind of paging register
But this is a limited solution, because most people will not want to mess with the internal guts of their 48K machine.
But this could provide some interesting features, like a shadow screen for a 48K (80K)