My friends fiancée had a similar problem a few weeks ago.
This is a copy of the letter I faxed to Immigration. It was not sworn but it was accepted. She had a copy of my passport and credit card as I had paid for the flight.
She flew the following day, paying 100$ for the change of flight.
Hope this is helpful
COPY OF MY LETTER
FAX .0063 2 8795917 13th November, 2008.
Chief Immigration Officer.
Immigration Dept, R.O.P. Manila
RE Miss Arleen Dxx, Passport No. XX.
Who was booked on PAL flight PR730 on 13th November 2008, flying to Bangkok, with a return ticket to MNL on 9th December, 2008.
The original ticket was booked by me on-line and paid for on my VISA credit card, No. xxxx xxxxx xxxxx 6826.
I subsequently changed the return date to 9th December Ms Dxxxx. I sent the money for the additional payment to Ms Dxx and she paid in PAL office in Makati.
The reason for the trip is to meet her fiancé Carl XXXXXX, a personal friend of mine. The couple were introduced by me and my Filipino wife and Carl stayed in Manila with Ms Dxxxx a couple of months ago. They are booked to stay at Asia Pattaya Hotel, room 7xx, 352 Moo 12 Pratamnak Road. Nongprue, Pattaya City, Cholburi 20150 Thailand. Tel : +66(0)38 250401-11 Fax: +66(0)2 215 9005
In January Carl XXXX will travel to Manila, with documentation to permit him to marry Ms Dxxx in early February, 2009. They will then apply for a visa for Ms Dxxx, then Mrs Arleen XXXXX, to reside permanently in Spain.
I hereby undertake and guarantee, to be fully responsible for all costs for Mr Dxxx for her holiday in Thailand and for her return to Philippines. She has travel insurance which was arranged by Carl XXXX.
(John Cxxxxx )
C/ XXXXX
29640 Fuengirola,
Malaga, Spain
Tel / fax (34) 952 xxxxxx.
UK Passport Number 70xxxxxxxxx Copy attached.
Passport copied here on Original