Allow subscription packages to use secondary group

[Cheule]

I'm really liking the subscription manager right now, except in one area.

The current setup means you have to create Group A for choice A, Group B for choice B and so on. What about allowing secondary group permissions to be "bolted on" to choice a, choice b and so on? Let me illustrate.

Current setup:

Gold Package
Gives you access to your own blog
Increases your PM inbox size to 150
Comes with 2mb of filespace to upload attachments
etc..

^^That is all you can do, if you want to add a similar package with less limitation, you have to create an entirely different package.

How about this (proposed setup):

Gold Package
Gives you access to your own blog
Increases your PM inbox size to 150
*increase PM inbox size to 250 for extra $1.50
*increase PM inbox size to 300 for extra $2.00
Comes with 2mb of filespace to upload attachments
*increase to 5mb for an extra $2.00
*increase to 10mb for an extra $4.00
*increase to 25mb for an extra $10.00
etc..

And so on. This way I can set up hidden subgroups with the increased permissions. :)

* = Denotes where a dropdown selector could be so that the user could 'tailor' the package to their own liking, and budget.