You will need to pass on the session-cookie, and re-set that cookie on the new domain. That will make the session live over several domains (assuming you use the same app).
Example:
Link from section1.com:
<a href="http://www.section2.com/?s=askdjh3k4jh234kjh">
then, OnSessionStart (or OnRequestStart) check for query-parameter s and attach session to it. Meaning, just manually set cookie ASP.NET_SESSIONID to the value you pass on.
This has severe security-implications, so don't allow this unless you know what you're doing. another solution might be to store something into a common backend (database?) and pass around the user with a token that represents the actual session (and set the cookie based on that token), that you generate on a middle-page when navigating away from section1.com -> transferusertonewdomain.aspx -> section2.com/?token=randomTokenThatMatchSessionInDatabase
That would prevent that anyone could hijack a session by jsut knowing the value of the cookie. However, that is possible never the less if you're somewhat familiar with a computer anyway.