Aggregation of licenses into one order

Hey,
has anyone ever tried to combine multiple licenses into one new order?

Let's say I sell webspace on a monthly basis.
A Customer now buys 1 license for a webspace today and two weeks later he buys another one.
They are both prepaid and synchronous, so on the date of purchase the they might not pay for a full month.
On the first of the following month he will be charged two times, once for each license.
But it would actually be better to only charge him once with the combined cost of both licenses.
Any thoughts on how to do that?

Cheers
bechtold