The phone call issue may not as large as you think.  Here are a couple of ideas:

1) If you have a direct dial number (no extension needed, customers can reach you using a 10 digit phone number (555) 555-1212) you can redirect the numbers form AutoTrader and your website to your extension.

2) If that is not possible, get a cell phone and redirect the numbers to the cell phone.  If you are unsure on how to reroute the phone numbers just ask vendor support for assistance.  The only cautionary flag here is that you publish your service number everywhere you have the sales number on your website since you will not be able to transfer incoming service calls from a cell phone.  Here again, Dealer.com should be able to assist you with setting this up.

Hi, so I am gathering that you have four major obstacles to overcome.  My suggestion is that you work with the owner to find out what their plans are and set proper goals.  If sales people want to complain you might want to just get a set few that will appreciate what you do for them and only give those customers to them.  Start a culture change and let everyone know how it will be.