When i first started making juice wines i used to add sugar to hot water in a pan to dissolve it, this needs to be left quite a while to cool before adding to a glass DJ, i now put the sugar into the DJ with the juice and use a combination of hot (not boiling) and cold water to bring it up to pitching temperature (just to the shoulder of the DJ) then i use my home made degassing wand to dissolve the sugar, this cuts down the time it takes to make a DJ of juice wine considerably (and the cleaning up afterwards)
Here is how to make one - http://www.thehomebrewforum.co.uk/showthread.php?t=48971
Here is how to make one - http://www.thehomebrewforum.co.uk/showthread.php?t=48971