it is my understanding that you can use any shimano shifter on those bosses, with a 4.5mm screw, but it may not look pretty.
BTW I have a frame with those bosses but the dropout is drilled for a Portcatena device crazy
__________________
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk