I have been following the various threads about using the scrlttr2 
class. However, none of them quite worked for me.

I have come up with the following hack using Babel. There are three 
files attached which illustrates the general principles.

* koma variables which don't change are defined in an LCO file.
* koma variables (toaddress, etc) which change between letters are 
defined using org PROPERTIES.
* a letter template in defined in a latex src block.
* The letter body is written in an org_mode src block.
* The final letter is produced by tangling the body, the lco file and 
the letter template.

In normal use you would simply modify the PROPERTIES and body text to 
suit each letter. The whole thing can probably be made into a yasnippet.

Suggestions for improvement welcome, as the existing stuff is just a 
quick hack.

Happy Christmas everyone and best wishes for the New Year.

Ian.