Can DHCP deamon expire leases "lazily"?

[Tom Horsley]

I've got some virtual machines with old kernels that know nothing
about virt clocks. They keep time so horribly when loaded up with
testbed runs that they forget to renew their DHCP lease, which
results in their name being removed from the DNS server, which
results in testbed failure :-(.

Does anyone know if it is possible to configure the DHCP daemon
to just leave expired leases active until it actually needs
to reuse the IP address for a new request?

Lacking that, I suppose I can identify the handful of machines
that exhibit this problem and give them static IPs...