Sounds like you want CDPATH. Given the following entry in .bash_profile,

export CDPATH=.:~:~/www:~/tmp
[download]

you get the desired behaviour with cd:

[~]$ cd bin
/home/ikegami/bin

[~/bin]$ cd lib
/home/ikegami/lib

[~/lib]$ cd example.com
/home/ikegami/www/example.com

[~/www/adaelis.com]$
[download]

It'll save you from writing a bash parser (although a half-assed one should work).