Ahh I see. I thought maybe we could work out something with DDNS or something simular. The problem isn't finding out what the range is NOW, thats doable, but rather how long it will stay that way. As the IPv4 pool becomes smaller and smaller, I have noticed the DHCP rotation increase, and sometimes entire new blocks opened or moved to different area's.
If security is more of a concern then the possibility of it not working, you can use ARIN to get the block. First, while at your second home, go to this site to find out your public IP. Then go to ARIN and enter that IP in top right corner search. The Netrange will give you the block of IPs your pulling from, but if you want wider radius, then click on the IP to the right of "Parent" and that will show you the whole range. This still isn't complete, but its something. Use at your own risk. 