Well...That is what they are used to asking for...a BP...I think something else would suffice...(ID, AC card etc) as it did in my case. The bottom line is if you are a member of the club (day pass, lifetime, annual, AMEX), you have the full access to what that club offers. They will just require another form of "collateral" so you can use the showers...

My denial at the IFL for showers is its only for "arrivals" on INTL flights so, one time...I got it...the other...no go....YMMV...But here at the Admirals Club, its not a restriction with this and you are allowed to use the showers...if you have the ability to enter the club....they just want their key back (like at a gas station back in the days), so holding some collateral gets them their key back!!