There is no direct documented way per my best understanding to achieve the dynamic route leaking of VRF Routes into GRT but there can be a possible workaround per my thought process as outlined below.
1. Create X/30 Tunnel Interfaces between PE-CE per customer peering and on the PE make the Tunnel Interface VRF aware ie part of the same VRF as PE-CE Interface using command" tunnel vrf VRF_Name"
2. Configure any PE-CE routing protocol of our choice under Global Config e.g eBGP over the Tunnel Interface X/30 and we can achieve the required import of Customer ROutes to GRT and send the GRT to the CE.
Caveats: This solution requires an additional X/30 between Each PE-CE Link to achieve the dynamic import behaviour but I would say this is not much of a burden as compared to achieving the dynamic behaviour.
I think with this approach you can acheive what you want (have the prefixes in global table and also in VRF table).
The other approach I remember using in the past is to have a physical loop on PE between different interface with one interface in global table and otehr in VRF table. Now configure ip address from same subnet and enable BGP between them. This way, you make the PE think that the neighbor is some remote addr instead of its own addr in different VRF :). You may have to take care of bgp router-id and allowas-in to make this work.
But to my knowledge, this is very complex and trafic may have to pass the physical loop. If you think the first approach solves your problem, it is better you use that.