How to place a charge using CHARGE keyword in Gaussian98

I am trying to simulate the electric field by point charge and need to place the charge in an appropriate position relative to the molecule.I have difficulty trying to do this.
 # hf/6-31G(d) Charge
 Title section
 0 1
 molecule specification
 <blank line>
 -10.000000     0.000000    17.320508 7.0
It is the last line that arises the difficulty.As my specification for the molecule is always in Z-matrix format,I do not know whether there is a convenient way to place the charge relative to my molecule(say,I want to it be 4.0A from atom1 and makes an angle 90 with atom1 and atom2 and a dihydral angle of 90 with atom1 and atom2 and atom3)
 From Gaussian website:
By default, the charges are read from the input stream, one per line, in this format:
 x y z charge point charge format
So if I specify the molecule in Z-matrix format,I do not know how it is converted to cartesian coordinate and how the charge is placed relative to the molecule.If I were to use cartesian coordinate for the molecule,it is not very easy to specify the charge position relative to some certain atoms.I am wondering if there is a good way of doing that.Hope someone can help me out.
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