My reading of that is that they want people to pledge money towards the project, but not to physically give it until such time as the HLF funding is secured. Although my personal view is that this will happen on the same day that Satan skis to work.
A part of a press release that I've read states something along the lines of "If we don't get the HLF money, we'll scrap the aeroplane". Hardly the best way to get the HLF committee onside, is it? The words "blackmail" and "emotional" spring to mind.