Is it possible to add more fields to \toaddress ?

The scrguien.pdf says that it's possible to define and add new fields to the reference block, e.g.

\newkomavar[desc]{newfield}
\addtoreffields{newfield}
\setkomavar{newfield}[desc]{ construction}

Is it or would it be possible to do something simlilar with the Addressee block. Currently this block consists of:

backaddress (return address)
specialmail    
toname
toaddress

In US commercial correspondence, it is common to add a barcode, which encodes the US postal zipcode, on either the envelope or the Addressee block visible through the envelope window. This barcode either precedes the Addressee (\toname + \toaddress) or follows it.

I would like to use UScommerical9.lco with mlabel.lco and use the envlab \PrintBarCode macro, ie.

\newcommand{\zipbarcode}{%
  \expandafter\PrintBarCode\expandafter{\citystatezip}%
}

I can of course hijack the specialmail field:

\setkomavar{specialmail}{\zipbarcode}

and (perhaps) swap the value of specialmailindent with specialmailrightindent

but, scrlttr2 still draws a line under the specialmail field
and it also sets the field rightflush (which looks wierd)

I just want the ability to print a barcode, either before or after the Addressee block. If I can remove the underline and rightflush formatting, the specialmail field would do.

Or perhaps some new commands like these are needed:
\newkomavar{uszip}{barcode}
\addtoaddressefield{barcode}
\setkomavar{barcode}[uszip]{\zipbarcode}
\KOMAoptions{barcodeposition=after}