No, you can’t
But: Yes, you can!
It is very(!) simple. Look at this example file: https://www.dropbox.com/s/yd19jh0y2gmwppl/accordion-staying-open.muse?dl=0
If you can’t figure out, how it is done, just ask!
Yes, it's a solution.
But pretty bothering, isn't it?
I think Accordion widget has more potential, could offer more options of customisation.
For example, it's annoying when your panels are pretty large and when you go from one to another, the accordion jumps and the user loose the beginning of the clicked panel.
Why bothering? Use the possibilities of Muse in a creative way! Why should they build in every function twice? Only, because users are not willing to use the existent potential? Muse is living with combining, nesting and integrating its element, and that is the only way to avoid interface clutter. In case of These cumulated accordions: There are tons of advantages compared to an integrated solution. Just think a little bit about it!
If you build such large accordions: Are you sure, an accordion is the best way to present your content?