Can I reproject WMS service using cgi parameters?

[Mark de Blois]

Hi all,
I am struggling trying to get a local WMS mapservice (local one with 
data in EPSG:4326) to be reprojected on the fly into a projection for 
which no EPSG code exists (Winkel Triple). But I am not sure whether 
this is possible (since there is not EPSG code for Winkel Triple I 
cannot add a WMS_SRS in the layer properties).

What I am trying to do is add onto the url for the map request:
 "proj=wintri&ellps=WGS84&lat_1=50&units=meters&BBox=-16000000,-10000000,16000000,10000000"
The result is the map in EPSG:4326 projection though zoomed out greatly. 
After changing the bounding box to -180,-90,180,90 I get my 'normal' 
lat/lon map though not in the projection I wish.

Could someonelet me know if what I am trying is possible at all? Thanks 
ahead!

cheers,
Mark