Hi Hannah,
Seems a good idea, but the forum might be a bit slow moving for last minute sailing.
The best opportunity for you at the moment, if you are available is a Friday evening. There are lots of people about but not too many to make it scary on the lake. The Officer in charge will be a one of the sail training team there is also a rescue boat out for added backup.
This session, 'Social Sailing' starts officially at 6.30pm but people basically turn up after work. It is very friendly and the club fleet is available free of charge to members. You must just give the OOD an idea of you ability.
I am thinking of putting together a buddy system to encourage double handed sailing more than anything. I was originally thinking of getting something going on a whiteboard in the club house. But I am sure we can sort something a bit more hi-tec for the website.