Nofollow script for SEO experts

After requested again and again from my SEO expert colleagues, I thought its high time to device something very basic but good tool fir my friends.
nofollow is an HTML attribute value used to instruct some search engines that a hyperlink should not influence the link target's ranking in the search engine's index. SEO experts want to build links for their pages and get their page ranked up high on yahoo/google/msn search engines.
you will get exact idea about how different search engine treats "nofollow" tag from following chart

rel="nofollow" Action	Google	Yahoo!	MSN Search	Ask.com
Follows the link	Yes	Yes	Yes	Yes
Indexes the "linked to" page	No	Yes	No	Yes
Shows the existence of the link	Only for a previously indexed page	Yes	Yes	Yes
In SERPs for anchor text	Only for a previously indexed page	Yes	Only for a previously indexed page	Yes

courtsey : wikipedia.org

The demand is that when server serves html to bot it should add rel="nofollow" to all external links. Another caveat was that it should not add nofollow to links whose class is "letmefollow"
The solution must be very easy to implement shud not require changes in existing code base php/html

I had played with apache filter in my previous projects . With new APR introduced in Apache2.0 output filtering became more easy and more clean and efficient. Also most of the hosting service provide with apache 2.0 provides mod_ext_filter module enabled in their installation. I deviced a very simple apache output filter using "sed" command. I had to use some advance sed options linke block, goto for this case.

So basically solutions was mainly doing following things
1) configure mod_ext filter
2) add environment variable using apache setenvif instruction
3) enable filter only for bots "bot" in User_Agent field of http request

If anybody wants me to know more on this then please contact me.