Charles, I think you could do some serious spotting with either a pen type thingy or a brush and the liquid Spotone type of product. You just need to fabricate a small spotting aid.

Take a flat piece of timber, say 75mm high by 15mm deep and 600mm long. At each end add a small spacer underneath, say 75mm high by 15mm deep by 50mm long, these are the feet. Attach some felt or something like that to the bottom of the feet, this aids in lessening scratches on your desk, or glass, or whatever.

The idea is to have your print flat, then you place your timber just above the area you need to spot, ensuring you straddle the print. You rest your hand on the timber, within reason, you should to be able to comfortably spot to the best of your ability.

I cannot tell you how easier it is with something like this, the effect is similar to using a tripod with your camera.