Since ER isn't VRF aware (yet...) you can't do this on a single device. You need multiple seperate interfaces each having 10.100.4.201 address. With VRF, you can partition a router sort of like you do with servers in VMWARE
ER-X is an option, if you got 8 of them, you can do without the ES48
btw, your picture got me thinking back to my printed circuit board design years 