I'm realizing now that another answer to your question is "No, there's not a way". In remarkjs (thus xaringan), every transition is an entirely new slide, including incremental slides.
For example, if you have an incremental slide with two bullet points
* Point One
--
* Point Two
creates two slides and is more or less equivalent to
* Point One
---
* Point One
* Point Two
It's not possible to have remarkjs come up with a different index for the slides. In other words, the two slides above will always be #n and #n+1. The best you can do is
-
Align the displayed number with the slide index (see above)
-
Give the first slide a meaningful name so you can jump to it
If you give an incremental slide a name, you can jump to it with #<slide-name>.
name: my-points
* Point One
--
* Point Two
And then you can jump to the start of this slide "group" by adding #my-points after the URL. It will automatically take you to the first slide of the incremental group. This has the extra benefit of being easier to remember, e.g. I have section on JSON in my slides that I can get to by adding #json to the URL. You can also have links in your slides to jump to those places.