I just found how to achieve this by using a workaround, sort of.
It's easy so I can spend a few minutes to tell.
Here's how to do:
In Math:
- Make your formula and save (for backup).
- Export into PDF.
In Inkscape
- Open (or create) a drawing where the formula shall stay.
- Create a new instance of Inkscape (referred as instance2 hereafter, as oposed to instance1 that contins the drawing).
- In Instance2 - FIle menu - Import pdf file.
- The whole contents in on place on canvas. Select it and Ungroup.
- Select the formula and copy.
- Shift to Instance 1. Important DO NOT CLOSE INSTANCE 2. Let it stay open until otherwise is mentioned!
- Select proper layer and paste it.
- You do now have a formula in your Inkscape document
Now you can close instance 2