Do Schengen rules allow the issue of a single entry-entry visa from Spain with a from/to validity period sufficient for an itinerary Cuba > Frankfurt > Madrid > UK, returning UK > Frankfurt > Cuba (airside transit) approxapproximately 6-8 weeks later, where the traveller would be spending say 3-4 nights in Spain on the outbound journey only?
If the answer is No, how can the itinerary be tweaked to avoid having to apply for a separate airside transit visa from Germany for the return trip?
Note: the traveller already has a UK visitor visa that would be valid until after the return via Frankfurt. In case it makes any difference, the outbound flight would be self-transfer in Frankfurt while the return trip would be connecting flights (one PNR).