Allow for multi-select

Howdy.
I’m doing a bit of customization, adding in a custom parameter to the shortcodes (thanks for using filters that allow this!)
However, I’m interested in creating a multi-select field. It’d be nice if the plugin did this by default; I realize I could use the bowe_codes_admin_shortode_build_form to do this, but since it’s just another attribute on an otherwise normal select, what would you say to enabling it as an attribute so I don’t have to duplicate the select element just for that feature?

Thanks!

https://wordpress.org/plugins/bowe-codes/