Groups with custom shapes?

Is there anyway to make a group to be a specific shape? Like say if you wanted a group to be in the shape of a triangle, pentagon, etc. I’m playing with an idea for a design but it requires having slanted/diagonal groups.

I did take a peek through the current plugins I can install and didn’t see anything right off the start that did what I wanted it to do.

My first thought is to simply use a background image of the desired shape. The group content would not be entirely “contained within” the shape, but it’s easy to implement and it doesn’t require any plug-ins.