Simbrief Flightplan - Starting outside the STAR

[TheSledge]

How do I start a flight at a specific fix along a complete Simbrief flightplan (EGLLKSFO) when the fix is outside the STAR? I want to land at the airport as planned but start a flight a few hours out from landing at a specific fix on the fp, using pilot WP (I presume). How do I set up FSIPanel so that it will e.g. erase all previous points in the flightplan (do I need to)? Thanks