Hi,
Actually, we've worked towards that goal last year with the addition of the "Characteristics dynamic display" setting in the HikaShop configuration.
With that setting activated, and with more than one characteristic attached to the product, you will have a please select choice for the second, third, etc characteristic and the add to cart button, stock, etc will only appear after that.
And with the next version of HikaShop, which is to be available before the end of February, that setting will be improved to allow to work with only one characteristic, and thus meet your need.