Controlling / Restricting Quantity Ordered

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-- HikaShop version -- : 2.3.0
-- Joomla version -- : 2.5.11
-- PHP version -- : 5.4.22
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We want to sell printed products that are only available in specific quantities from our supplier, but I don't see an easy way to control or restrict the quantity / increments a customer can choose.

Ideally, I envision a combo box presenting valid order quantities, such as:
250
500
1000
2500
5000

...the standard "+" and "-" buttons would not be presented when only specific quantities are valid.

I found a post where it appears the intended functionality could be implemented with considerable modification:
www.hikashop.com/forum/4-how-to/82422-qu...vascript.html#105072

However, I wouldn't want to modify core code and potentially have to modify with each release of Hikashop.

We considered adding duplicate products with the quantity being a package price. In this scenario, instead of ordering 250, the customer would order quantity 1 of "package of 250". But even that wouldn't work as there are increments our supplier doesn't offer. Using the same scenario, we could not present "package of 1,000" because the customer might order 2 packages, and the total quantity of 2,000 isn't offered by our supplier.

Is there any chance this type of functionality / control may be implemented in Hikashop at some point?