We had the same dilemma and decided that instead of paying for anchors to be installed somehow it was easier and more convenient to buy a second Britax Carseat. Sure, it cost $250, but now we each have a seat and if my wife needs to take a neighbor to or from a playdate along with our kid, we have two seats.

In addition, the LATCH anchors or ISOFIXs (same thing) ar eonly recommended up to a seat and child combined weight of around 40 pounds or so. After that most instructions tell you to use the belt anyway to attach the seat.

Get a second seat, you'll be amazed how you did without one after you get it.

Jim