AFAIK FME currently doesn't have an out of the box way to do this (dynamically processing data within multiple arbitrary datasets) within a single workspace. If they implemented this feature though, you could do it with a FeatureReader: http://fmepedia.safe.com/AnswersQuestionDetail?id=906a0000000coPaAAI
It has to be initiated by another controlling process, e.g. another workspace, a batch script, a Python script, an executable, etc.
One possibility that avoids using a controlling process might be using a PythonCaller and reading the datasets using the FME Objects API and the
Basically you would read the Excel spreadsheet with an FME reader as usual, send each row of that spreadsheet into the PythonCaller, and the PythonCaller would read the MapInfo file specified by the current row and output the features of the MapInfo file to be subsequently processed by other transformers or writers.
I haven't tested this but it should be possible.
The next obvious problem then would be writing to multiple arbitrary datasets, which is also not possible with a single FME workspace. This I think is going to be much harder, but again, probably possible using the FME Objects API. For that reason I tend to stick to using a controlling process.