Generating unknown words

Is there a way to generate with the ERG from an MRS that has an unknown word?

For example, I can parse “the stumpy tree” but “stumpy” is unknown:

[ TOP: h0
  INDEX: e2 [ e SF: prop ]
  RELS: < [ unknown<0:15> LBL: h1 ARG: x4 [ x PERS: 3 NUM: sg IND: + ] ARG0: e2 ]
          [ _the_q<0:3> LBL: h5 ARG0: x4 RSTR: h6 BODY: h7 ]
          [ _stumpy/jj_u_unknown<4:10> LBL: h8 ARG0: e9 [ e SF: prop TENSE: untensed MOOD: indicative PROG: bool PERF: - ] ARG1: x4 ]
          [ _tree_n_of<11:15> LBL: h8 ARG0: x4 ARG1: i10 ] >
  HCONS: < h0 qeq h1 h6 qeq h8 > ]

Would adding something to the SEMI be enough?