Key signature in ossia?

[Nick Payne]

How can I add a key signature to an ossia stave? In the example below, I get
an error if I uncomment either of the key signature lines in the ossia
staff.

%===========================================
\version "2.12.2"

\new Staff = main \relative c'' {
        \key e \minor
        c4 b d c
        <<
        { c4 b d c }
        \new Staff \with {
%               \set Staff.keySignature = #`(((1 . 3) . ,SHARP))        
%               \key e \minor
                \remove "Time_signature_engraver"
                fontSize = #-3
                \override StaffSymbol #'staff-space = #(magstep -3)
                \override StaffSymbol #'thickness = #(magstep -3)
        }
        { e4 d f e }
        >>
        c4 b c2
}
%===========================================

Nick Payne