Was in Philippines late 03 early 04 for about 4 months.
Found a place which was suitable. In fact lots of places but only tried it out in a couple of places.
On Luzon Island head for Dagupan. From there take bus either to Hundred Islands. Stay on the mainland and then take bangka boat out to one of the islands and ask boat man to drop you off a small secluded beach. I went nude there so I know it's possible.
Another place where it's possible is in the same region. Go to Bolinao and take a trike to Patar Beach. It's 17km long. Very few tourists. The further away from town the less people. Again I went nude there briefly.
Anything's possible in the PI. Also did a fair amount of jungle walking with one of the hash clubs. We went places where it would be possible to get out into nature and be naked such as rock pools in the jungle etc.