RedirectMatch ^/basedirectory/exceptiondirectory1(.*)$ http://server1/basedirectory//exceptiondirectory1$1
RedirectMatch ^/basedirectory/exceptiondirectory2(.*)$ http://server1/basedirectory//exceptiondirectory2$1
RedirectMatch ^/basedirectory/(|[^/].*)$ http://server2/basedirectory/$1