I assume your B2 is running the unmodified Excito software and underlying Debian squeeze, right?
The main problem is support for Debian squeeze ended this year.
You can try to user the "-t wheezy" option to specifically search the wheezy repo and "-s" to only simulate the process.
Dhcpcd5 might depend on other packages that are too old in squeeze and also have to be imported from wheezy, which could then break other old squeeze packages because they don't work with newer libraries you've just installed for dhcpcd5.
At that point, upgrading the whole System is a better idea.
But a) you cannot use the wheezy stock Kernel and need one patched for the B2 (same on B3) and b) it most certainly will break the Excito software suite on it.
Some people in this forum are developing newer images for their B2/3s though, but you might have to bend over a bit to get to the same solution that you are having now.
I use Mouette's Debian jessie-1.0 image (
Link), but that comes without a Software suite.
Alternatively there is the Bubbagen live-usb by Gordon (
Link) that has a replacement Software suite, but is based on gentoo.
Either way, if you want dhcpcd5 on your B2 squeeze, you need either luck, or a bit of elbow grease, or be ready to drop some services.