I think, at this point, that you would have to go in and edit the file used during registration. This isn’t a good method, though, because that means when BuddyPress updates, your changes will be overwritten.
I have switched back to the default permalink structure. It has to be a bug – as changing the permalink structure back to /%category%/%postname%/ will fix the members page, but break the blog. Changing to the default fixes the blog and breaks the members page.
#blog-details-fields span.suffix_address:after {
content: "Please choose a name for your blog and click Signup to complete registration.";
display: block;
color: #555;
}
input#blog_title {display:block;}
Basically, this changed the dialog to “Please choose a name for your blog and click Signup to complete registration.”. This way, the user could still select the name for the blog, but was never prompted to create the blog and the subdomain of the blog is the user’s username.