We did this with Watermelon Vodka, thinking that it might complement the grapes and add even more of a summer vibe. Very nice for us. Substitute a splash of bubbly for the soda if you want to go a bit posh.
The grape, ginger, basil and lime flavours marry extremely well and are very refreshing and original. I reduced the sugar syrup by one third to make a less sweet version as I enjoy an edge of tartness. Increase all the base quantities proportionately and pour into a long glass with ice and lots of soda water - this makes for a superb and distinctive outdoor summer cooler!