how can I modify the datepicker to show months only?

how can I modify the datepicker to show months only?

What I would like to do is the following:
  1. I would like a the datepicker to show only months (month names), no days.
  2. once the user selects a month, I need the date for the form field to be set to the last day of the chosen month.
I asked a question yesterday that is related to the same project, and it works - as soon as the user picks a day in the chosen month, I can manipulate the chosen date to get the last day for the month and then set the date for the datepicker to the calculated last day of that month. However to avoid confusion forn the user, I would like them to pick only the months instead, if at all possible.
Obviously I can use CSS to hide the days in the calendar, but that doesn't select any dates...

Any help very much appreciated!