Get a block of wood and drill a hole in it same diameter as the connectors (5mm I think). Push the connector down into it until just the last little section that you're soldering the wire onto is sticking out the wood. This way, when the solder runs, it won't run down the connector. Any excess around the soldered end can just be filed down (again easier when it's in the block of wood). Also use a little less solder so less overflows when you put the wire in. So long as the wire and the connector are tinned beforehand, you'll still get a good solid connection.