I've had this question posed a few times and i really don't know how to answer it. I don't think any of the cigar tobaccos are particularly "sweet". In your opinion, what is the sweetest cigar filler we have?...or how can a cigar be made to taste sweet?
Of the WLT cigar tobaccos I've had so far, I would say the maduro wrapper has the most sweet taste in the flavor profile, with the dominican binder coming in second, and the sumatra binder/wrapper third. Not filler I know, and not many would use expensive wrapper as filler, but I use the maduro, dominican and sumat scraps as filler for that specific reason.
I have noticed that my short scrap filler cigars are noticeably sweeter tasting, being the greater part binder and wrapper inside and out. The same effect is achieved by rolling smaller gauge (38 or less) long filler cigars bound with dominican and wrapped with sumatra.
Various casings/toppings could be used ala Swisher or FX Smith, but assume the question is how to do this with unadulterated leaf.