I think your best bet is to try to push that first A time hun. At 5.5 months we really had to push our A times to as close to 3hrs as we could manage so we could get through the 3-2. If you aren't doing school run during winter break this might be the best time to really try to ramp up that first A, as you won't risk any car naps.
The other thing we did was a short/long/short routine, because I found that 3 naps was too much, but 2 was not enough. So if you do get a short first nap, do about a 2.5hr A time for the next one and hope for a long nap, and then add a short CN in late afternoon. That said, I think that pushing that first A as much as possible is really going to get you through and push the whole day later, so hopefully you can achieve 2 good naps.