I did some tests, and found that the following script works:
set("number of periodic groups",3);
set('periods',[100;500;100]);
set('start cell group', [1;3;5]);
set('end cell group', [2;3;6]);
this will create a device of cell1-cell2 with 100 periods, cell 3 with 500 periods, and cell-5-cell6 with 100 perdiods.
Please test and see if it works for you. You may use matrix variables instead of something like this [100;500;100]. eg, period=[100;500;100], then
set('periods',period);