Your first problem with be that most universities will have minimum periods of candidacy so you are unlikely to be able to enrol somewhere for a year to complete for example. More seriously though if your research involves human subjects as I imagine it might well do, then not having ethical approval for your specific project will make it very hard to get a supervisor to take it on part way through. Finally, as an employee you probably do not own the intellectual copyright to the research data you are currently using, so it may not be possible for you to use it in a thesis unless your current employer agrees. The simplest way would be to see if you ca enrol as a staff candidate where you are working - the fees are often low in that case - and use your PI as a supervisor.