Variable as widget argument? (Sugarcube 2)

So I don't know if this can be done: I'd like to make a widget that sets a variable to a particular value, and lets me choose which variable every time I use it. But I can't do:
<<widget mywidget>><<set $args[0] to "something complicated">><<endwidget>>
and then
<<mywidget $specificvar>>
Because that would just pass the current value of $specificvar to the widget, which obviously wouldn't do anything. Is there some way to work around this?