Firstly kudos on your patience and determination with Silicon Milk Roundabout. I've been a remote admirer of the project and I hope at some point I'll be able to engage more directly with the project, not least when it comes to our (www.kayako.com) own hiring. Silicon Roundabout and everything else associated with it is something I feel strongly about.
As far as reaching out to CS and engineering (etc) soon-to-be-graduates, have you been in touch with computer science and engineering faculties in universities, making an introduction and asking for them to send an email out to students?
Even easier would be to contact the social/ents society for the CS department/engineering faculties. Those societies will be more willing to send an email blast about careers events like these.
For example: http://cssbristol.co.uk/ http://www.cs.ox.ac.uk/societies/COGS/ http://www.cs-society.co.uk/site/
Another idea might be the British Computer Society. They have a Young Professionals Group (I've posted about SMR to the LinkedIn group), and the main body of BCS would probably be more than happy to help with promotion.
Hope this helps and apologies if it was all already obvious and tried.
Edit: Seems I am late with a couple of those suggestions. Oh well, I'll keep thinking.