How about a F-20 with some of the developments of the late model F-16s? E.g avionics spine and/or conformal fuel tanks?
That could get a bit problematical in some ways, given the internal structure. If I was going to add a conformal tank, I'd work it around the centerline pylon on the underside of the aircraft, though you'd also need to stay clear of the MLG bays and doors. You could modify the existing upper fuselage somewhat, but you've got that heat exchanger intake at the base of the vertical fin with a hydrazine bottle for the remote start system aft of it.
I still think I'd look at a larger wing to reduce the wing loading to something a bit more reasonable; keep the existing tapered planform and tip chord, but enlarge the root chord and extend the span, possibly adding another stores station under each wing.