First of all, you will have to make sure you are present when the orders are sorted. You should be doing this regardless in case there are problems or confusion with the orders.
The most obvious thing to do is to put re-order stickers on all your products if it possible. This does not take away from the fundraiser and their efforts but may help you to get more orders. You may be able to convert some of those who bought simply to help the organization or those that had never heard of the product before to become customers. You never know when someone already knows and loves the products but is looking for a new consultant. So make sure you put those labels on!
Check with the organization to see if you can put business cards in the product bags. This may or may not be acceptable with them so ask before assuming. You may want to ask about this in advance when you are in the planning stages as you may need to order more cards depending on the size of the order.
If you can do business cards, you may want to offer an incentive as well. Create business cards or a coupon that says if they have a party within 30 days of the date (stamp them with the date they are to be delivered) they will get product A for free or half off, whatever incentive you want to offer. You could also offer an incentive if they were to book their own fundraiser within 30 days.
Do you do something different to try and get more business from a fundraiser?