Is there a way to copy the assignee automatically to the watcher list?

[Marya Calaunan Magno]

I have created a plugin that will copy the assignee to the watchers list via the Edit Issue screen. However, the feature we want to achieve is to copy the assignee to the watcher list via the Assign screen (the window that pops up when Assign button is clicked).

Questions:

1. Is there any other way to achieve the feature without purchasing any add on?

2. If the only way is to do our own plugin, what context should we use in atlassian-plugin.xml? Can you provide links to help us in this plugin?

We really appreciate your help! Thanks a lot!