Exclude host from default scheduling policy?

Hi there,

I want to remove a host from the default scheduling algorithm, so that machines are only scheduled to it when a requirement matches.
I know I can set a requirement that is only matched by the remaining hosts, but unfortunately I have too many running instances that I do not want to modify.

To clarify:

Cloud with host1, host2, host3;
Host3 has GPU=true
Only machines with a requirement for GPU=true go to host3;
Machine without any requirements are scheduled between host1 and host 2.

Is this possible?