need advice pinning down existing drip cap

The aluminum drip cap on the front of my house needs to be pinned down. There are not enough nails and the ones that are there are not driven down tight enough. Didn't really notice until I had seamless gutters installed. Gutter goes behind the drip edge and the brackets are then screwed through the face of the drip cap.When the mounting brackets were screwed in it caused the top of the drip cap to buckle up in spots. So I need to pin the drip cap down to the roof without removing or damaging the existing shingles. Any tips or tricks from you pros?
I'm also wondering if there is another way to attach the gutter brackets (maybe a different type) to avoid the drip cap? Thanks.