What's the elevation of the stock ATGM mount? I'm thinking of the crude way of simply replacing the MILAN launcher with a MANPADS.
A good friend of mine was a Marder commander. I'll ask him when I see him the next time. But I don't think there is much in the way of elevation. The ATGM mount on the Marder is just a kind of clamp that fixes the Milan and associated bits by clamping the normal folded-up tripod to the vehicle. There are a couple of really good pics in
THIS WALK-AROUND. I also don't think the Milan launcher proper can elevate that much. With the way the ATGM mount fixed in place on the turret, I don't think there's much lateral movement either. Anything apart outside of 11-1 o'clock and you really have to twist yourself out of the hatch.
I just remember that the SOP for firing the Milan from the vehicle includes swinging the turret to the 11 o'clock position and depressing the 20mm gun all the way.
If you want to have the MANPADS power-operated from within the vehicle, I suppose the best bet is to fix a Stinger or two to the external MG3 mount on the turret.