Economic Order Quantity w/ no set up costs Is it possible to modify the EOQ model to work in a purchasing environment when ordering costs are effectively $0$?

The classic EOQ model is:
$$
Q=\sqrt{2aK/h}
$$

with $a$ being demand, $K$ ordering costs, and $h$ the holding costs. If $K$ is $0$ it yields an order quantity of $0$. Is there any optimal way of determining the order quantity when there are no order costs?
The total ordering cost are 

$TC(Q)=P\cdot a+\frac{a\cdot K}{Q}+\frac{h\cdot Q}{2}$

If K=0 TC becomes

$TC(Q)=P\cdot a+\frac{h\cdot Q}{2}$

P\cdot a is a constant. Let denote it as c.

$TC(Q)=c+\frac{h}{2}Q$

You can see that TC is a straight line with a slope of $\frac{h}{2}$ and a domain of $Q \in \mathbb R^+$. The marginal cost is 

$\frac{dTC}{dQ}=\frac{h}{2}$

It is a constant. Therefore there is no single optimum order quantity.

The store has a capacity. This is the upper limit of the order. If you have still some goods in the store the maximum order is the capacity (c) minus the goods in the store (x).

Therfore you can order bewtween $0$ (exclusive) and $c-x$ (inclusive) goods. The total cost of inventory will be always the same for a given demand in a period.