Role based security on field

Hi all,

I am using CRM 2011. I have following business scenario:

I have added two new custom entities. ONe is master and another child. You can say, same as Opportunity and Opportunity Product. What i need is, based on security role, i need to show/hide child entitity's tab on parent entity.

I have googled it and folund following two options:

1) Add different forms for the entity and assign security roles on that. Customize forms accordingly.

2) Enable field level security. And do required settings in Field Security Profile. But in this option, i can set access level for users/teams only. Can we have any option for Role here?

Anyone, guid me on proper direction?