Temporary lines for filling border?

[snowforest]

Addition: If there was another object inside that selected layer, it gets covered so beware. For example I wanted to apply the method again for an area, in which I had a plus sign. When I applied the steps above, the plus sign also gets covered with the fill. I had to do the fill in the usual way then, on original layer, where we can select the area with the fuzzy select tool, which can exclude the pus sign....