Equivalent one-output of a SIMO converter
Switches S1 to Sn direct the stored energy to one out of the n outputs i.e. the switches act like a  demultiplexor so if you want to model a single output then insert a time delay after the charge and discharge part of the switching cycle. Put another way, if there are ten outputs then each output only gets serviced in its allotted cycle and the rest of the time is just dead time so if the charge discharge cycle last 10 us wait 90 us until beginning the cycle again.

I’m not going to consider what happens if there is still energy in the inductor when the cycle starts for the analysed output because it gets messy.