~/.rpmmacros:

%argtest(p:b:a:) %{-b:b=%{-b*}} 1=%1

$ rpm -E "%argtest -p 1 -b 2 param1 param2"
b=2 1=param1

$ rpm -E "%argtest param1 param2 -p 1 -b 2"
 1=param1

thus, if parameters are passed before options, the options are not to be seen

rpm 5.0.2

-- 
glen