Would something like this do perhaps?
====
\version "2.19.81"
\score {
\new PianoStaff
<<
\new Staff = "right"
\with {
fontSize = #-6
\override StaffSymbol.staff-space = #(magstep -6)
}
\relative c'' {a4 a a a \bar "|."}
\new Staff = "left" \relative c {\clef bass a4 a a a \bar "|."}
>>
}
====
Out of interest, why do you want a smaller staff for organ music RH? Just curious.