I found out how in the end, you see the two pillars next to the big circular platform that is also a part of it? You want to jump as high as you can on the one on the left, and try and keep jumping. if it works you should be able to get a jumping placement enough for you to get o n. Careful not to drop down though. I went down to mop up the last few guys I could not see due to them hiding below it and almost died, so have a plan for any one who hides there. (; And do it quick, Xur leaves soon and you still need to hand him the urn.