A/B switch for Two 240V connections into Electrical Panel
Assuming that your load calcs were based on actual load and not breaker sizes, the DPDT switch idea has merit. What I would look at though is the physical location of the loads. For example is your 240V dryer in the garage? If so, then I would put the DPDT switch in there to feed either the dryer or the car charger (assuming the sizes match), because you are going to manually connect the car anyway, so you throw the switch when you make the connection. It does mean not running the dryer and the car charger at the same time, but you are going to be giving up one load in any case.
What I would get is called a &quot;Double Throw Safety Switch&quot;, like a disconnect switch except the handle is On-Off-On, as in Dryer up, Off in the center, Charger down.
This is a picture of a 3 pole version, you only need a 2 pole, but it gives you the idea.