ONIOM DFT/AM1 calculations with Osmium

I am trying to calculate a large molecule using a hybrid method. The
 molecule contains an osmium tetroxide plus a large organic
 residue. The procedure will involve an ONIOM calculation using a small
 DFT region plus a large semiempiric region. However, the ONIOM method
 requires that the whole molecule be described by the low method, AM1
 in this case. The problem arises when I try to calculate the whole
 molecule using AM1.
 To my unluck, not only is Osmium not parametrized in Gaussian98.A9,
 but the VSTO-3G basis does not suppor athoms greater than N=54 (osmium
 has an atomic number of 76). To make things worse, looking inside the
 code, every athom with N>54 is exchanged by Xe in link 301. But Xenon
 is described without d orbitals, and therefore I get the following
 error:
 ========================================================================
  (Enter /QFsoft/g98/l301.exe)
  Standard basis: VSTO-3G (5D, 7F)
  Atomic number  76 exceeds maximum of  54 in STO -- maximum used.
  There are     5 symmetry adapted basis functions of A'  symmetry.
  There are     1 symmetry adapted basis functions of A"  symmetry.
  Crude estimate of integral set expansion from redundant integrals=1.000.
  Integral buffers will be    262144 words long.
  Raffenetti 1 integral format.
  Two-electron integral symmetry is turned on.
      6 basis functions       18 primitive gaussians
      5 alpha electrons        5 beta electrons
        nuclear repulsion energy         5.0493269225 Hartrees.
  Leave Link  301 at Fri Mar  8 18:49:55 2002, MaxMem=    6291456 cpu:       0.1
  (Enter /QFsoft/g98/l401.exe)
  Simple Huckel Guess.
  NBasis=   6 NMin=  11 so simple Huckel guess is impossible.
  Error termination via Lnk1e in /QFsoft/g98/l401.exe.
 ========================================================================
 Link 401 complains that not enough basis functions are available. Do
 you have any hint how I could solve this problem?
 Many thanks in advance,
 --
     Galí Drudis i Solé
     gali (+ at +) klingon.uab.es
      Universitat Autònoma de Barcelona
      Unitat de Química
      Lab: C7/157
      Tel: +34 93-581.28.14
      Fax: +34 93-581.29.20