you can pump two diffirent current say 1uA and 10uA in two different BJT.
use relation VBE1 -VBE2 = nVt*ln(I1/I2).
so you just nedd to take the difference between two voltage and do a temperature DC sweep.
it should be simple linear line..as expected (Vt=kT/q)
you can take derivative to get dVt/dT.
hope mathimatical funtions are available in the simulator..