When I replaced the external teak handrails on my O'Day with PlasTeak, I used the original teak rails inside as pictured. I thru-bolted the inside and external rails together. That is also how the rails on my current Catalina are done. If you can find ones that match the same loop size as the ones on the outside, I'd get new bolts and thru-bolt them together. Very strong and you don't have to drill new holes.
You can get stainless rails too if you don't want more wood, or replace the external rails with PlasTeak or Stainless and move the current rails to the inside.
As mentioned by a previous poster - DO NOT SCREW THEM IN . Even if you don't PLAN to use them as actual handholds, you never know when you or someone else may need to grab hold of the first thing that comes in reach...