I don't exactly understand your situation but from what I can comprehend - That's a toughy. To be honest with you, I'd stay away from that campaign if you're not using your own domain.
The first entry for the term "trademark" within one dictionary source (Oxford American Dictionaries via Mac OSX Dashboard) says "a symbol, word, or words legally registered or established by use as representing a company or product". A company legally registers and/or establishes a domain name usually for the purpose of representing themselves and/or their products on the internet.
Unless someone here says, or points out, otherwise, I'd try looking for another ppc campaign. Maybe if you clarify and/or elaborate your post in other words, you may get someone with better knowledge of this to respond. Goodluck!