I haven't personally tested these designs, but others have and found them to be satisfactory. I would still appreciate some feedback. Please mail me.
The method appears to be based on an equation in J. Hall, "Off-center loaded dipole antennas", QST Sept 1974, 28-34.
I am grateful to Craig Pennington, NC4P, http://nc4p.com/antenna-theory, for identifying this source and spotting an error in the original program which I have corrected in the current version.
Hall does not give a derivation. However, an apparently different method is described fully by L. Duarte Lopez, "Designing a shortened antenna", QST October 2003, 28-32. I have also programmed this but find that it gives inductor values about 40% higher than this calculation. (Thanks to Skip Behnke, W2OZ for this information.)
This corrected version installed 19 Sept 2003.