also set up your VPN to push /2s if this relies on /1s,

I don't think this is a smart way to mitigate this because it could easily result in an arms race. Push /2s, the attacker will switch to /3s; push /4s, the attacker will switch to /5s, etc. Every +1 is going to require doubling the number of routing table entries.

That can't continue forever, obviously, but it's going to result in a negative experience for the user if the VPN client has to push hundreds or thousands of routes to mitigate this attack.