I recall a thread last year that claims dive shops in Puerta Galera have a "liason" that extends the visa of divers, ....
I've had a reply from the Sabang hotel :-
Any VISA extensions and other concerns related to it can be solved and done in Puerto Galera through our immigration consultant.
Russ.... be cautious if you use this. It would probably be ok.... BUT....
There was a similar scheme running in Thailand a few years ago. 'Consultant' service that ran your passports over the border for renewal. After a couple of years successful operation, the Police decided to crack-down on it. Of course, the consultant got away with it. The tourists had the passports impounded... upon summons to collect them, they were imprisoned and then deported. Scary...
The difference was that in Thailand, it was a border-run (stamp out, stamp back in).. in the Philippines it is a direct renewal. One thing about the Philippines is that 'routine' practices may actually be technically illegal etc... again, you may get unlucky and get caught in a 'crack-down'. The same is true of a myriad of issues, including safety ones. The short lesson is "don't believe anything you are told in the Philippines, if common sense says otherwise".
As I say... it's PROBABLY ok... and is probably above board... I should be near the Subic immigration office later this week. If I have time, I will go and inquire about the 'consultancy' services for you.
Also... be cautious with your passport... I'd want an awful lot of reassurances before I handed my passport over to someone in anything other than an 'official' capacity. Take photocopies of it. Take scans of it also...and email them to yourself, so you can always print them out. Make sure you have the contact number for the UK Embassy in Manila, just in case. Get some form of official receipt from the hotel and get some assurances when you hand it over... if they lose it, they won't admit it, or take responsibility.