Calendar Invitations and Multiple Email Addresses?

I am a consultant, so I need to set up meetings/events (and send invitations) using different email accounts. Some need to come from a biz email, some from my personal.

I've still been using BusyCal as my default calendar, as it enables me to choose which "originating email" to use each time. I've read a lot of threads on this, but it appears that even w/ Mountain Lion, my Mac Calendar still must send all invitations from one default email account. Is this true?? I'd love to use OS X Calendar -- but this is a huge show-stopper for me. It's actually hard for me to believe that Apple would've set it up this way, in today's world of multiple email accounts (work, personal, volunteering, etc.!) -- so I'm really hoping there is a work-around for this. HELP!