Here's a guess. The IDG cooling system dumps the hot fuel from the fuel cooled oil coolers into the outer tanks. If you start the right hand engine first (sops with most airlines) the RH IDG oil temp will reach it's dump temp before the LH and thus increase the temp of the fuel in the right outer tank. Sounds good techno waffle to me and i'm sure i'd convince most pilots that I know what i'm talking about.
