No, you should still use filterRLS = 1. You just need a row per sales territory/user in the filter table.
The measure is evaluated per row of data being displayed in your visual, so as long as there's a single row in the filter table with that sales territory/user combination the measure should still evaluate to 1. This is working for me in my proof of concept.
I think what you want is to have a slicer that shows only the sales territories that the logged-in user is allowed to see, that you want to do that by showing the sales territory in the slicer and filtering the slicer using the filterRLS measure. Problem is that you can't put a visual filter on a slicer.
There may be some kind of hack or workaround, but not one I'm aware of off hand. Best I can think of is instead of a slicer, having a table that lists all the sales territories and when the user clicks on a row in that table it filters everything else on the page.
Unfortunately not that I know of. That is a huge problem with this approach. It's more a Row Level Suggestion than actual Row Level Security - a convenient way to pre-filter a report for users, but not true security.