Seems like just the taxi light should be sufficient during a long
descent at low power... What do you expect to see at 3000 feet, or
whatever? I only turn a light on that high up so others can see me...
And, landing lights are vastly over rated as far as usefullness...
There have been studies that show that leaving the landing lights off
and using the runway lighting gives better depth perception...

Now, having talked all around the subject, no I don't know of a 'legal'
replacement switch that will give you only separate lights because even
if it were 'legal' in another airplane it won't be 'legal' in yours
because it wasn't certified with that style of switch... So, my best
advice is for you to find a switch that will fit, and will operate the
way you want, change it out yourself, and move on...

denny