Get a piece of chair rail or some other molding (moulding in UK and and elsewhere). Bang it around until it's all dented and chipped. Run a brush of paint (white is okay) up the wood, painting it heavy in some spots and light in others. Sort of measure the wall and sort of cut the molding to length. Nail it up on the wall, but don't worry about it being level.

Go all gushy over the work like that that's been done on the house, "why s/he even did the wiring his/her self!"