For an alternate approach to pull off this challenge- while it may sound counter-intuitive at first, what if we were to make Europe richer, more populous and more united, from an earlier stage in history? I'm thinking along the lines of The Carolingian/ Holy Roman Empire ITTL paralleling the development of the Mughal Empire IOTL. With the relatively poorer, less politically unified, but still more militarily advanced Africans ITTL having already turned their attentions to sending naval trade expeditions between Europe, India and the Far East, after having been largely cut off from the Silk Road (by the Muslim Conquests, which still happen ITTL, but are significantly less successful in Africa than they were IOTL. Even so, the Islamic conquests are still sufficient for the Islamic Caliphate to seize control of the primary Silk Road trading routes between China, India, Central Asia- and ITTL, all the way through the Balkans into Central Europe, due to Europe's increased wealth and trade importance), African state-backed merchant conglomerates begin to establish critical trading ports with the Carolingian rulers of most of Europe (ITTL, due to the greater extent of its integration with the rest of Eurasia, Europe is perceived to be a sub-continental region of Eurasia rather than a continent in its own right, in the same way that India is IOTL).
Expanding commerce during Holy Roman Imperial rule gives rise to new European commercial and political elites, along the coasts of southern (Mediterranean) and eastern (Balkans & Black Sea) Europe. As the Holy Roman empire eventually disintegrates ITTL, in a manner akin to the decline and eventual disintegration of the Mughal Empire IOTL, many among these elites are able to seek and control their own affairs, and break away to form independent kingdoms- with the respective African trading companies' control of the seas, greater resources, and more advanced military training and technology making the allegiance of their fledgling nations with the African trading companies become increasingly attractive to a portion of the European elite. This proves to be critical to allowing the African companies to gain control by proxy over critical regions, such as the Spanish and Italian archipelagos - and their further access to the riches of these regions, and the subsequent increased strength and size of the African trading companies' armies eventually enable them to annex or subdue virtually all of of Europe.
Does that sound more feasible?