As an ol' kamaina, and one who regularly plays a uke-strung tenor banjo for some local morris dancers, the uke tuning of G C E A, sung out as "My Dog Has Fleas" (the G being one whole note below the A) is the equivalent of putting a capo on a guitar's fifth fret and playing the four highest strings. In this case, the guitar "D" chord will now be a "G" chord for the uke-banjo, the "C" chord will be an "F" and the guitar "G" is now "C", etc.

The uke-stung tenor banjo tuning of D G B E (D being one whole note below E) is the most common, and you will simply use the guitar fingering of the 4 highest open strings (keeping in mind the treble "D" string is one octave higher than it's guitar equivalent).

So grab the uke, sing out "My Dog Has Fleas", tune to your "song", put one finger on the highest string at the third fret, (a "C" chord), stum con gusto, and Tiny Tim goes muttering to his grave...