I think Zoraster's suggestion on letting them out of ruins is a pretty good idea but you don't actually have to let them take toll. They still have to break through the hole in the wall. Just Throw nades and rockets right outside to make them stay in the alley way. That way you still lighten the load on ruins and gain a better chance on break through. If not put rockets and nades in the hole in the wall closer to ruins and trap a squad that's an easy 5 tickets.
If the EU commander is intelligent he knows that ruins is impossible to get through once it's locked down and he has able SLs he can just order his team to just stay put and the bait doesn't apply. If that happens there is only one way to use the road to your advantage to take ruins even if their walker is there although i never have the SLs to try this out. The idea requires an able commander and smart but gutsy squads. You will also need a good walker squad. Make sure you mine bait just a little bit of the road past the blockades and push your walker in close enough so that the top gunner has an eye on the left side where ruins meets the alley way and spray to kick up dust and scare off the defenders while the main pilot sprays at the feet of the gated area to screen off that area. Then you need at least 4-5 squads attacking different areas of ruins at the same time. you need 1 squad to move down the alley way and then go left then 2nd to go on the main road and push into the hole between the downed gunship and wall and join up with 1. Then you need 3 to go past the down gunship and make a left to the ruins entrance that faces the road.Then you need to put an emp infront of the enemy walker. The idea is to make him back up so he doesn't have any visual to chew up your infantry. At this time CO needs to drop an orbital at wherever EU infantry is massing to counter to either block them or kill them this is probably near the gateway where there is about one squad throwing rockets down the road. Then you need 4 to push down the road and get to the back of EU at which point your orbital will be near its last few rounds and they can push in without taking too much friendly orbital fire. If you have that 5th squad they can take the topside route to get on top or ruins. Or if they are awesome enough and your other 4 squads don't need the extra hand you can have them go topside to outpost. When your first 3 squads have made it to at least the entrance ways get your walker out of their asap because that enemy walker won't stay back there forever and your walker will be your only line of defense if EU tries for a counter attack while you are attacking them. If all goes well which it probably won't without extremely disciplined units you will have ruins surrounded on three sides and they will throw most of their guys north to 1 & 2 and then 3 will forced them to shift a few to the side so 1 & 2 don't get overrun and then 4 will catch them from behind while your orbital shields 4s approach and the emp will either stop or back up the enemy walker making it ineffective for that 6 or so seconds and your 5th squad if you have one will give you an insurance or a leverage incase 1-4 need a hand or if they fail but EU is all at ruins and you take outpost from behind.

NOTE: I have never done this but i've always wanted to because it seems plausible.
WARNING: If you do not do this moments after and enemy Orbital you stand the likely chance of losing 2 or more squads and failing completely.