FileMaker Portal Sorting Using Value Lists
FITCH AND FITCH on a portal sorting method using value lists to set up the sorting:
The great thing about this technique is that all the logic and control is script-driven, which makes it easy to set up and to make changes down the road. You will not be incurring technical debt.
This technique can be extended in all kinds of fun ways with conditional formatting, script triggers, etc. You can even allow your users to do a custom sort. Yes, a custom-sorted portal! See the example file for a basic implementation.
There are some interesting comments in the original post, as well.
FileMaker Portal Sorting That Doesn’t Suck™ | Fitch & Fitch.