For a form of government which is more "alternative," consider Samoa IOTL as a model. Since the death of Tupua Tamasese Mea'ole, the Samoan head of state is elected every five years, but (a) he has always been one of the four paramount chiefs, and (b) he is referred to by a royal title - "His Highness" - rather than a republican one.
This kind of royal republic could work very well with West African elective monarchy. Most of the traditional Nigerian kings, for instance, are selected by a college of "kingmakers" from a pool of several royal families: the Ooni of Ife, for instance, can come from any of four houses. It's possible to imagine this system writ large as a form of national government - in addition to its parliament, a country could have a house of kingmakers with no other function than to elect a ceremonial head of state, and the head of state would be called by a royal title during his term of office.
One problem, of course, could be that many modern African states have a multiplicity of traditional kings - Nigeria has more than 70 - so which one would get to be head of state? OTOH, Malaysia has solved that problem pretty well IOTL, and a national college of kingmakers that rotates the position between the traditional monarchs could work. What we'd need, probably, is for this form of government to be set up during the later colonial period, for instance if the British try to balance out an expansion of the franchise by giving more power to traditional rulers who support their interests.