Nick Hancock, 37, from Ratho, is preparing to head to the isolated islet of Rockall – 225 miles west of the Outer Hebrides – next month.
Only four people have ever slept on Rockall, while fewer than 100 have landed on it.
Mr Hancock hopes to spend 60 days on the rock to raise money for Help For Heroes.
He said: “I need another £12,000 for the attempt to go ahead and I am fast losing hope. If I don’t raise the money in the next two weeks I will have to call it off for this year.
“I hope that somebody will come forward but all the companies I have approached have basically said ‘it’s the recession’. There’s no spare money about for something like this.”