Orders shipping much later

I have a client for whom I am creating a site. They are selling outdoor plants which will only ship at certain times of the year. The client wants customers to be able to pre-order items throughout the year but not be charged until they are ready to ship. - This is mostly wholesale to nurseries, garden centers etc.

Having read through quite a few threads, I do not see anyone doing anything similar. Originally my client was expecting to take credit card details as the order is placed and charge when shipped. This is normal practice but in this case, the time between order and ship may be several months.

PayPal does something called Authorization & Capture but that is limited to 29 days. Google Checkout has a similar time frame. Using something like Authorize.net costs an arm and a leg and could not be justified for this client.

I am going to suggest to my client to have customers place orders without credit card details and then invoice them closer to the shipping date.

Questions:

1. Has anyone done something similar whom I have not yet found
2. Is my suggestion the best (only) option
3. What modules would I use to set for an order only situation but to be able to go back and invoice later.

I am thinking #3 to be built as an incomplete order where we are able to send an auto-responder and then completing the process later, probably by sending the order as an invoice.

Has anyone any ideas on this? I am completely open to suggestions. Thanks.