An alternative to the Compaq is one of the other Safe N Sound convertibles - the Haven, Trojan, Guardian, Safeguard etc. They have the same shell as the Compaq, but have a different base, which makes them 5cm shorter. I bought a Compaq recently and found it too tall to use FF in my car (we have 3 across too). I could hardly see out the rear window, so I returned it. I'm getting a Trojan instead (on sale this week at Target).
You may find you can fit 3 in your Pulsar while they are all in convertible seats, but it might be impossible when you need to use a booster and need access to the seatbelt.