you can use an omni light that only affects specularity, to simulate it when using GI.
remember that the max specular highlights are no physically correct approach. radiosity simulates real-world lighting. to get real specular reflections/highlights you have to use raytracing and very bright object-lights or hdr-images.
read this article:
http://www.neilblevins.com/cg_educat...l_and_refs.htm