Boosting voltage from a current source
Well, a solar panel is not a perfect current source. If the load has a high impedance value, your solar panel can't generate a high enough voltage to provide \$I_{SC}\$ otherwise It should be to generate unlimited amount of power.


  when the switch is connected vertically (on state), the steady state current over the inductor doesn't change so its voltage is zero.


Assume we're in the boost steady state. Before connecting the inductor to solar panel, the value of the current going through it decreased  since it was releasing its energy to the output. When you connect it to the panel, the current has to jump instantaneously to \$I_{SC}\$ which means the panel has to generate an infinite voltage, not possible. The voltage across the panel (equal to the voltage across the inductor) has a finite value. You calculate \$I_{L}\$ using integrals until is reaches \$I_{SC}\$ then it maintains that value.


  Can I just smack a capacitor of the right size in parallel between the solar cell and the boost converter?


That's is a good idea to make the panel work in a specific operating point (voltage and current generated by the panel are more stable because of the capacitor charging/discharging) which I'm guessing is the MPP. Otherwise they will be varying a lot and your controller will be struggling if it was able to work at all.

PS: This is quite a simplistic approach I made just to get the point across, if you want precise calculations, be prepared to use a bit more of maths \$(e^{f(V)})\$ :P