ASA 5505 initiating a tunnel?

For our clients who do not have VPN devices we program and ship a VPN device to them. We have been using Nortel Contivity 1010's, but are looking to migrate to Cisco ASA 5505's. The 1010's have a setting called "nailed up" that causes it to continuously try to build a tunnel. This works great for clients who have DSL or Cable with a single public IP address. Even though the 1010 is connected on the inside LAN, NAT/PAT with the public is not a problem b/c of the nailed up feature. Does the ASA have something similar? I tried usuaing NAT-T but that didn't seem to help. There are probably changes I could make on the DSL or Cable routers that would make this work, but we don't want to have to change the client's enviroment in any way.