Do you still have the Lowr unit? If the wpts have been cleared from the L unit, then simply import the .usr into the unit, and export as .gpx. If existing wpts in the unit are from other sources and you don't want to mix, first save these wpts, and then delete. Load the .usr you want to convert into the unit, and export as .gpx. Then import to HBPC. Clear wpts from Lowr unit and import original wpts to restore this unit as it was.
If you don't have the Lowr unit, see if a buddy with Lowr Gen 2/3 will let you do the above. I have Gen 1 and it doesn't save in .usr v5.
You might also try GPSVisualizer - but I don't think it will work for .usr files, at least the newer versions because Lowr went to proprietary versions back some time ago.
I know many will snicker at this, but I am pretty good at this conversion stuff. If you want to send me the file via email to try and convert for you, PM me. I will promise to not retain your info - just trying to help.
LOVE GOLD Jimmy