Not a cheap option.
But the best as far as granted levels go.

A is the parent account.
B-X are the RAF accounts.
And you are only keeping A when you are done.

Have A refer every account.
So it looks like this:

A -- B
A -- C
A -- D
A -- E

Etc.
You only want to get the chain to 5 toons, as that is the group size limit.

Now for the "not" cheap part.
Transfer a toon from A to B.
This is your booster.

The A -- B link will generate no RAF.
And Account B will not be gaining levels.

However, the A -- C, A -- D and A -- E links will be RAF links.
And while you are losing granted levels from B to A.
You are gaining a level 60 toon on A instead of 30 levels granted from B, for every 60th you boost.

And A still gets 50% of the levels gained by C, D and E.

Note, A and B need to be on the same B.Net account, or there is a 30 day hold on transfers.
Since B-E are disposable accounts, you would not want CDE to be on your B.Net account.