Cookieless session, but session ID as a query string

[Hope Paka]

Normally if you enable cookieless attribute in session element, in
web.config your url becomes like
http://domain.com/(SESSIONID)/Default.aspx

This is really good if you are not considering search engine spiders. Each
time they enter to your site, they got a different URL. This means that you
can never have a good page rank you your site.

I need to use session id like,
http://domain.com/Default.aspx?sessionId=(SESSIONID)
ASP was supporting this, but ASP.Net only supports in the way i have
explained.

What should i do for it?
Are there doc. about custom session implementation ?
Or any idea about this?