Allow Watchers to be added/View to issues on a project without browse permission for the entire project

Hi,

Simple case scenario, We have multiple user groups in our organisation - typically 3 main Groups (External, Business & Technology)

Sometimes we have projects which have sensitive information on them, when this happens it would make sense to set the Issue level security to this:

Current Assignee, Reporter and Watchers

As an example: I send a request to HR for an Increase where my payslip is attached where the assignee in is someone in HR, but we need my Boss to be a watcher who can comment or approve. In this case the only people who should see this issue would be myself(Reporter), the HR assistant (Current Assignee) and my boss (Watcher). But the problem is that now multiple people have browse access on the Project and can also see my payslip - This makes for a failed HR Support Project?

Please advise?