Show Order Lines for all Orders on the Order's Account?

Hello:

I am not sure if this is possible, but wanted to find advice from the community:

I want to show the cumulative quantity on the Account of all Order Lines from any Order associated to the Account.  My thought would be to create a new entity ("Products Owned") as a N:N of Order:Order Line, then a 1:N Account:Products Owned and show a sub-grid on Account.  Are there any special rules, etc. regarding Orders, Order Lines, etc. that would prohibit this?  Is there an easier way?