Best way to persuade ISP to trial SPF?

Hi all- 

I've just set up a test SPF records on my personal domain, but as my 
broadband ISP rewrites the sender address of email I send through their SMTP 
servers, I use a third-party authenticated SMTP relay service in the UK.  I 
wrote a friendly email to the SMTP provider yesterday saying that I'd just 
started trialling SPF and would they consider it, and got this reply: 

"Thank you for your mail regarding spf.  We will of course look into your 
request but as with any new technology we would not be able to adopt it 
without serious testing and investigation into its effects/side effects." 

I did give them a handful of links to SPF information, but has anyone 
perhaps got something they've sent to their ISP which is polite but yet 
persuasive?  I have a nagging feeling I might be the only one so far who's 
requested SPF, so they're not likely to do anything.  Something along the 
lines of "<big-isps>.com implemented SPF already..." 

:-) 

Thanks, 

James