Running several planets "on the same IP" obviously is a problem MHs and players have to deal with. Exceptions may result in "limited legal multying" while still having legal players be deleted which seems to be a rising concern/problem.
To give legal players coming from the same IP increased certainty/protection, i suggest to create a stand-alone client which simply consists out of two functions:
a) implement a WWW-widget/gadget (potentially limited to *.planetarion.com)
b) implement a function to either check if another instance of this client is running on the same machine or create a unique string from a machines configuration and send it to a script on the PA servers which make sure no two matching configurations are allowed on the same IP (multying) or alternatively just log the unique string for a MH to check on later.
So anybody who would want to be safe from beeing "accidently" deleted for multiing because they are on the same IP like somebody else (who they probably dont even know about), can use this client software to play a planet instead of using a generic browser where these kind of checks may be impractical to implement. The MH's could use the knowledge that somebody uses this client instead a generic browser in their judgement.
It takes a rather small amount of work to do such a client in a language like VB but for portability i would suggest using something like PureBasic which enables you to offer a very small native binary executable for download on Windows, Linux and Mac OS X systems compiled from the same source. Those systems should cover over 95% of all players. It doesnt interfere with any other PA development and therefore can be added and removed anytime without problems.
Downsides:
It wouldnt stop a multi from the same IP using one machine for each planet or using something like VMWARE to run the tool on the same machine but both of these actions are a rather harsh penalty in infrastructure to run multiple planets
ps: and in theory if all planets from the same IP use this client, they shouldnt be restricted anymore in interaction which enables fully cooperative play of housemates, workmates, classmates etc. again. In schools/Uni you may have a problem though as people usually can use several computers at once and run a client on each of them.