04 Venture Keyless entry park lights & Horn

I bought a 2004 Venture and the park lights and horn won't work. The Chevy dealer said the van was a rental and they chose not to have that feature install on the van. Is there some way that I can reinstall the feature without haveing to buy a new BCM unit.

No, if you don't have the right BCM, you would have to purchase a new BCM.