I think there is a bit of a misconception here.
Blurb wants the images to be in sRGB color space. In Lr you can softproof to sRGB.
Blurb also provides an icc-profile that can be used to softproof the images. Alas, this icc-profile is a CMYK profile and is not usable in Lr. Lr is RGB-only and doesn't work with any CMYK-profiles. But you can use Blurbs icc-profile for softproofing in Photoshop CSxx.
If you don't have Photoshop CSxx, you can't use Blurbs icc-profile and your only optin is to softproof to sRGB. Since you have to embed sRGB in the photos used in your Blurb book, softproofing to sRGB will give you a good match.
On their website Blurb recommends these steps for Color Management: http://www.blurb.com/guides/color_management/workflow
What they don't mention and possibly the most important thing is that the intensity (brightness) of your monitor is not to high. Some people have complained that their images in the Blurb book are too dark. The reason for this is that their monitors display the images too bright, i.e. brighter than a true representation of the color numbers. But since printers go by the color numbers, you get a darker print.
Make sure that the intensity (brightness) of you rmonitor is set to a value of about 110 cd/m2.
Finally, read this thread: http://forums.adobe.com/message/4360009#4360009
and particularly Andrew Rodneys post (# 11).