Sebastian,
          An adhesion promoter would probably not be to good for PDMS to metal
bond.  Plasma sounds best.  I suggest a mild Argon plasma use a capacitive
system then the plasma field will be uniform parallel to the electrode and the
tops of the pillars will get good mild adhesion.  In my experience a plasma
density of 1 watt per square inch and 5 minutes of argon plasma will produce
water contact angles close to zero or the best adhesion chance.  Bill Moffat