If it was me at this point, I'd talk to him.  "Friend you said you are going to bid on that property.  If it goes for more than you want, would it bother you if I started to bid, when you stop if it's in my budget range".  Then you can gauge his reaction.  
My friends and I, when it came to auctions, was first speak-first pick.  The first one to mention it got to bid until it got to high.  Then the second friend could bit if he chose.  I worked really well.  A guy I know would bid against his friend unknowingly, because they were so secretive, they wouldn't talk about what they were going to bid on while they rode together to the auction.