What I normally do for all 3rd. party VPN (because so many "features" are missing on the MX for this), is use another firewall, like a good old ASA, for the 3rd party VPN.
Then I create a small route net between the HUB MX and the ASA and create a static route on the HUB MX for the VPN networks.
The static route can be distributed into AutoVPN.
Of course, now it might now also be possible with the new MX19 software and eBGP over IPSEC.