You can set the electrical on-resistance, Rdson, however, this is not directly linked to the lookup table data for conduction loss, and is anyway fixed value (non-temperature varying/dependent).
We use lookup tables to calculate the conduction loss (or using an equation defined in the thermal description), so while a physical/electrical on-resistance could have a small but non-zero influence on the currents that a device "sees" such that the resultant conduction loss lookup can change slightly with different electrical resistance values, the electrical and thermal domains are effectively parallel. The electrical on-resistance rather could be useful for looking at current sharing conditions or providing dampening, and if one doesn't provide a thermal description (or specifically data for the conduction loss), the on-resistance is the only way that a device on a heat sink component can have its conduction loss calculated.
But I don't fully understand your question about the Rdson curves, and wonder what your ultimate goal is? Are you just saying you have Rdson vs. Tj and Ids data, but not IV curves directly? We may be able to provide some suggestion if you clarify what you really want to achieve.
And let me know if anything I said was unclear.