I have a bunch of already-assembled drawer boxes and need to sand the insides before spraying. I want to use my triangular-shaped power sander, but don't want that little trench you get on the adjacent surface. Festool now makes plastic edge protectors for these sanders (see photo), but they don't fit mine because it's an older model. Could I use a drywall knife or something similar to protect the surface I'm not sanding?107007290_662750071254088_5617074344826741865_o.jpg