Use flat sheet gutterguard, not roll.
Put the gutterguard up in place, drill holes in the hard flat bumper area that the gutterguard contacts and use screws and washers to secure.
Use small, discreet wire-ties or something to secure any remaining areas where possible.
That's it - 5 minutes, your done. The top grill was much much much much much harder with acid etch, color match, dremmel, clearcoat, mesh cutting, etc.