You can delimit values using $, ....eg if you have 5 checkboxes all called "my" with values 1 2 3 4 5 then you could do:
local $, = "|";
and then $in{my} would look like 1|2|3|4|5
local $, = "|";
and then $in{my} would look like 1|2|3|4|5