Along with the other suggestions (automation, compression, HP, EQ), I'd push the harmonized leads about 25-40% out from center on each side and then also automate the 80% panned rhythms to drop a wee bit to give the leads some additional room in the chorus or whatever...Or, you could automate them to pan to full 100% on the chorus, opening up the area between hard pan and center a little bit. Automating the pan might also give a bigger sonic weight to the sides, making the stereo image open up a bit, which could have a nice dramatic impact.