First off this should be in the persistence forum.
You thinking in object land. How would JBossCMP map this type of property to a set of columns? It can't, but it could use a map table that has a name column and a value column.
Ok, you need another table, so you need another bean. Create MapEntryEJB with only a local interface, and name and value columns. Then setup a one-to-many relationship between YourEJB and MapEntiyEJB.