In "Napoleon Mercenaries", without providing a name, Guy Dempsey guess that the officer could be from the french Hanoverian Legion, present at Bussaco.

Unfortunately I don't have the list of officers of this unit. The names of wounded and killed officers of Hanoverian Legion in Martinien (below) does not include the three that you listed.

Either this is not the proper unit, or this officer was never wounded. Or the story was embellished, and an hanoverian legion officer inquired about a former colleague, not a brother, with different name.

Also, did you check the deceased of 5/60th after Bussaco ? Contrary to the french habit, who gave time for units to collect their men, english report of a battle was done almost immediately, and did not include the wounded who died in the following days, lowering the casualties. So more names could appear.

Legion Hanovrienne, infantry:
Killed before or at Bussaco: Weyhaupt, Spange, Bourgoing, Gargam, Koerdel, Boecklin
Wounded, or killed after Bussaco: Liebhaber, Blum, Hermann, Stamm, Sauer, Weniger, Saalmuller, Goesman, Deroth, Mang, Zwenger, Schelver, Seligmann, Ihmoff, Simmler, Schmidt

Legion Hanovrienne, cavalry (no casualty at Bussaco i.e. not present or unused due to the montainous terrain):
Killed before Bussaco: Schmit, Eberhard L, Eberhard A, Scharloock
Wounded: Doldenel, Spielberg, Decker, Frépini, Someiller, Gourvello, Lacourte, Burgel, Decetto, Bagger, Lux dit Schneider, Fleddermann, Kretschmann