You might want to ask customer service that question. I don't think that would work since the day you activate the card is the day your billing cycle begins and are charged and I think if you activate it outside of the promo expiration date you might not get the discount.
If you are getting a new number with the plan and not porting in you could get the card close to the end of the promo expiration, get the discount and when the card shows up activate it in your phone so service is on and then get a phone for the card would work. Bad thing is if you are not getting a phone until middle of June you would be paying for service and not using it to get the discount.
Chance are Visible will have another Promo when this ends but not guaranteed though. The discount for the $5/$10 off have been running since late February the latest one I think is number 3 now and notice this one a person doesn't even need a promo code like SPRING the last one had.
