computational chemistry - Gaussian: Relaxed scan with modredundant optimization and dummy atoms

I would like to perform a relaxed scan in Gaussian09 on my molecule using the modredundant optimization. Because I want to scan over two bond lengths simultaneously, I defined some dummy atoms which are close to the real atoms whose bond lenghts should be scanned. However, this approach does not work, because I can't properly index the dummy atoms. The Gaussian09 documentation says (emphasis mine):

[Type] N1 [N2 [N3 [N4]]] S nsteps stepsize [[min] max]]

N1, N2, N3 and N4 are atom numbers or wildcards (discussed below). Atom numbering begins at 1, and any dummy atoms are not counted.

How can I then perform a scan referencing a dummy atom? I don't want to do the scan using the z-matrix optimization because it does not converge.

Here is my input file:

%nprocshared=16
%mem=5gb
%chk=4MeAminoButanal
#P HF/6-31G(d) opt=(modredundant) scrf=(pcm) nosymm

4MeAminoButanal dummy scan

0 1

 C     0.000000     0.000000     0.000000
 N     0.000000     0.000000     1.451901
 C     1.325038     0.000000     2.055476
 C     1.991320     1.377897     2.032970
 C     1.229182     2.449098     2.809397
 C     1.309917     2.335179     4.306919
 X    -0.248373    -0.404008     1.611583
 X    -1.041414    -0.131882     1.066579
 H     1.218960    -0.323776     3.083767
 H     1.990264    -0.714465     1.564774

 H     2.993872     1.281489     2.436811
 H     2.106328     1.711600     1.006802
 H     1.602469     3.443240     2.566292
 H     0.178120     2.455789     2.536445
 H     0.708887     3.065770     4.854632
 H    -1.016528    -0.113770    -0.358506
 H     0.375985     0.943036    -0.379032
 H     0.606031    -0.798850    -0.431982
 X     1.641992     1.939406     4.607116
 X     1.311963     2.318294     5.471711

 O     1.974063     1.543637     4.907309
 H    -0.496745    -0.808017     1.771266

B 7 19 S 60 -0.05
B 22 7 F
B 2 7 F
B 6 19 F
B 21 19 F

When I run it, Gaussian09 obviously complains with

The following ModRedundant input section has been read: Invalid atom number. B 7 19 S 60 -0.05