I had the same problem.
Whiteline do make a rear camber kit, haven't seen or heard of anyone using these.
I ended up getting a set of adjustable rear arms (where to suit a Gen IV BL/BP, but have the same set-up) of a Group Buy on LegacyGT.com



The arms are the front of the rear (the straight ones), and adjust toe and camber.

They are a copy of the HKS (I think it was HKS...) adjustable arms, but cost 1/4 of the price.

Mine got adjusted to almost all the way in (there is maybe 25mm of thread both sides of the adjusting nut), so if you did a track day you could wind in some huge negative camber.

i work at repco and im pretty sure we sell camber kits fo rthem, cause i remember looking up for my car on suspension stuff and think i saw a camber kit listed for it, mine is a gen 3 wagon too

Whiteline part number is KCA399.