Ken

Try gently prying the siding off. If the nails will not give, slip a hack saw blade up behind the siding and cut each nail. Maybe a long flexable fine-tooth sawzall blade would work but you risk damaging the clapboard if the blade binds up while using the power tool.

Jim

I've had good success on removing square nails (nailed into Doug Fir) using the pincer type "slam bang (similar to a dent puller, but in reverse) nail puller. Positioned just right they leave 2 slight dimples on either side of the nail. If the siding is soft you may need to use a pad under the fulcrum arm. Wear gloves to avoid massive blisters.