5 entities that I would like to display in one grid...

I have 5 entities that I would like to display in one grid. I would like a single or double-click on a grid row to open a different form for each entity. The 5 entities have a set of fields in common and then a larger number of fields that are unique to each entity.

I am attempting to avoid a single, combined entity that holds a superset of all the fields. The reason I am avoiding this is to improve database performance (the single entity could have 1000+ fields, eventually) and to avoid writing hide/show logic. 

I am also trying to avoid having a separate grid for each of the 5 entities so I don't have to add a new grid every time I add a new entity (which will happen a couple of times a year).

I working in CRM 2011.

Any ideas on how to accomplish this?

Many thanks!