Se puede utilizar jinja2 o algún otro manejador de templates para cambiar el .map en tiempo de ejecución y de esta forma poder enviar algún parámetro adicional para realizar cambios en el servicio WMS o WFS.

import web
import mapscript


# URLS
urls = (
    '/','Basic',
)


class Basic:
    """Layers Basics
    """
    def GET(self):

        vars = web.input()
        if len(vars)==0:
            return info_layer(Basic)
        req = mapscript.OWSRequest()
        for i in vars.keys():
            req.setParameter( i, vars[i])


        map = mapscript.mapObj('basic.map')

        mapscript.msIO_installStdoutToBuffer()
        map.OWSDispatch( req )

        content_type = mapscript.msIO_stripStdoutBufferContentType()
        content = mapscript.msIO_getStdoutBufferBytes()
        web.header("Content-Type","%s; charset=utf-8"%(content_type))
        return content


    def POST(self):

        vars = web.input()
        req = mapscript.OWSRequest()
        for i in vars.keys():
            req.setParameter( i, vars[i])

        req.postrequest=web.data()
        req.type=mapscript.MS_POST_REQUEST
        map = mapscript.mapObj('basic.map')

        mapscript.msIO_installStdoutToBuffer()
        map.OWSDispatch( req )

        content_type = mapscript.msIO_stripStdoutBufferContentType()
        content = mapscript.msIO_getStdoutBufferBytes()
        web.header("Content-Type","%s; charset=utf-8"%(content_type))
        return content

app = web.application(urls, globals())

#web.internalerror = web.debugerror 


if __name__ == "__main__":
    app.run()