Bitmask to boolean conversion in the model

I have a model that receives int bitmasks from the backend:

{"user": 7, "group":5, "other":1}

and I now want to show a form with checkboxes like this:

user:   [X] read [X] write [X] execute
group:  [X] read [ ] write [X] execute
other:  [ ] read [ ] write [X] execute

where user can toggle on or off and then the updated bitmask is sent back to the server in a store.sync operation.

I know how to make and align the checkboxes, but ExtJS checkboxes in a form bind to boolean values through a correlation between the checkbox name and the model field name, and not to parts of bitmask.

So I have to convert back and forth between the bitmask int and a bunch of booleans. How would I implement that in a reusable manner?