Date of first Assignment and maipulating the Assign action in a workflow

Aside for the regular bug tracking tool, we are using Jira as a field support tool which is under some strict SLA requirements.
The first step of handling an issue was to assign it to the handler (it was created unassigned by default).
I couldn't find a way to get the First assigned date, aside for creating a custom field,
teaching the users not to use the 'Assign' button (that does not appear in the workflow) and to create another transition that will populate the custom field I have created.
This solution is messy and includes educating users.
I was wondering if I was maybe missing something with the use of the events (that maybe I can catch the 'Issue Assigned' event and use it to populate the field.
or maybe there is a date field that I have missed.
But if I didn't I think it will be an improvement to be able to play with the 'Assign' action in a workflow and not just permission or notification wise.