This page lists the things not allowed at each trust level.
To get mojoPortal to work in partial trust we would have to remove or disable all use of System.Reflection.
In branches/2.1 I have already removed most use of relflection in creating the log4net log object
Before the syntaxt was like this using reflection:
private static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
and now its like this:
private static readonly log4net.ILog log
But theses changes have not been released yet (until later this weekend) so the only way to get them right now is from svn which may also require use of db upgrade scripts since there are changes since the last release. Be very sure to back up your site and your db before you try this.
I'm not sure this will completely solve the problem of partial trust. You could try this and it may still give the error, I don't know.
More recently, for use of 3rd party web parts, I use Reflection to loop through assemblies in the bin to find installed web parts. This may not raise an error if you don't use this feature though, I'm not sure.