[NTG-context] Tweaking an existing letter style

I am typesetting a letter using Wolfgang's letter module. I have a requirement that deviates from any of the existing styles, namely that the recipient, i.e. the address, and the sender, i.e., the header, need to start left and right respectively and at the same height. I am using the modified style and am trying to adjust the layout via he \setupletterstyle command without success. I have look at the sources and have seen how the elements of the various styles are stacked, but I cannot discern how to achieve the side-by-side arrangement I require. If anyone can advise me how I can move these various layers about, I would be very grateful. Cheers, Michael