Yeah this.... I used a floor Jack which was slightly precarious but worked out ok.^ If you don't have a buddy to help either hold or cut, you're going to want some kind of jack to hold up the bumper.
Plan to go through several rounds of trimming and fitting, then pulling everything off and trimming again. This is the tedious part.
Also keep the fasteners loose enough to wiggle the bumper until you have all the bolts/nuts/fasteners in place and aligned where you want. Once I was happy with my cuts, I wasted a bunch of time tightening the passenger side. Then realized I had to undo everything to get the driver's side lined up.
Post pictures! Want to see it on that blue