Hi there,
The easiest solution would be to buy yourself a cheap Cisco ISR. Configure a Layer3 interface ('outside')and connect it to your ISP modem/router so that it is on the same IP subnet.
Configure the additional subnets on the ISR for the purpose of your lab. Configure source NAT to translate the lab subnets behind the 'outside' interface.
This will mean that lab traffic is NAT'd twice; once by the ISR and then a second time by the ISP router. However you will not need to worry about bridge config or any static/dynamic routing.
cheers,
Seb.