Path Selection with OSPF external routes VS "O" routes

We have couple of route based site-to-site vpn with cost/priority configured on the Fortigate 500 D firewalls and its working fine. So we are adding layer 3 (Active and Standby )connectivity through the service provider MPLS network where we need to connect our Head Office and Data Center. We are running routing protocol OSPF with my Fortigate 500 D with PE Router to make OSPF adjacency. During implementation we found that the routes we are receiving from provider PE router  is E1/E2 routes. Our goal was to use Active layer 3 connection through MPLS will be Primary Link and and Standby one will be Secondary if primary one fails. We put the cost on the Active link 3 and Standby 6. Although we put the lowest cost for Active and Standby Link  compare to our existing route based VPN(Cost starts from 10 and onward) nevertheless traffic is NOT passing through the Active and Standby Link. I think this is because as Fortigate 500 D  sees the Layer 3 routes as external routes. I know that regardless of a route's metric or administrative distance, OFPS will choose routes in the following order: Intra-Area(O)-->Inter-Area(O IA) --> External Type 1(E1) --> External Type 2 (E2) -->NSSA Type 1(N1)-->NSSA Type 2(N2) etc. So, is there any way to show provider external E1/E2 routes as "O" (OSPF) routes in Fortigate 500 D.  If I can do that then I can put cost on all those "O" routes and make the Layer 3 primary one as our primary link. Any feedback will be appreciated. 

Thanks.