Disable input text but not disable calendar?

Bug description:

Is there or can we have a way to disable the input text box but still allow the calendar to work? Currently if the input text is disabled, it disables the whole calendar, but really I just want to prevent users from typing in the date box.

Link to minimally-working plunker that reproduces the issue:

http://plnkr.co/edit/c53OivUuETsY9eN7AE5V?p=preview

Version of Angular, UIBS, and Bootstrap

Angular: 1.5.8

UIBS: 2.1.3

Bootstrap: 3.3.7