[texhax] Advanced Ligature Handling in .pl Files

[Stan]

I would like to use some of TeX's (Metafont's?) smarter ligature  
capabilities (described under the headings "smarter ligatures" and  
"boundary ligatures" in the article  
www.tug.org/TUGboat/Articles/tb10-3/tb25knut.pdf) in fonts for which I  
already have .tfm files.  I've successfully specified some ligatures  
("ff", "fi", etc.) using what I learned from this page:

http://www.slac.stanford.edu/comp/unix/package/tex/web2c/web2c_10.html

but this page does not talk about the more advanced ligature handling.  (I  
used tftopl on the .tfm file for the font in question, added some entries  
to the ligtable, and then converted the .pl file back to a .tfm using  
pltotf.  This process worked for "standard" ligatures.)  I tried  
variations on the syntax specified in the Tugboat article, as well as on  
pages 316 and 317 in appendix F of The Metafont Book, but that doesn't  
seem to be for .pl files.

Is there a way to specify the more advanced ligature handling in .pl  
files?  Also, are there any other resources that discuss the syntax to use  
in .pl files?

Thanks for any help.