Multisite Calendar without using having to force users to post events in Buddy Press

Trying to figure out a way to make this happen...any help is greatly appreciated.

I have a site with multiple blogs...each blog has 1 or 2 bloggers who keep their blog/site up to date.
I am looking for a calendar plugin that will allow them to have their own calendar but will also post all dates to a main calendar.

I know this is very similar to GroupCalendar but I am trying to figure out how to do this without having to force each blog to also have a group....or more importantly for them to have to leave the admin panel and go to the BudyPress groups page to add their event. The folks posting the content and calendar items are non-profits and aren't very tech savvy.

Thoughts?

Thanks in advance!