Answer: If you're that close to the line, you probably have some Zone 5 winters and some Zone 6 winters! Fortunately, there are plenty of hardy evergreens that are hardy to even colder regions, so you're in fine shape.
You may be able to restrict the size of the pines you mentioned by using root pruning techniques. This slows the growth of woody plants by reducing the amount of roots available to supply moisture and nutrients (think bonsai!). I think you'll be better off in the long run if you choose tree varieties that have a full, squat growth habit rather than trying to force a quick-growing tree to slow down.
Try instead red cedar, Japanese yew, or hemlock varieties that you can shear regularly to keep them full to the ground and maintain the proper height. Some of these grow in excess of a foot per year! Check with a local nursery for the types that are best suited to that microclimate of yours. Be careful to purchase healthy specimens - this time of year, nurseries may not have "fresh" stock available, so shop around for the best. Also, prepare your soil well beforehand, so you can plant the shrubs immediately after purchase. Best of luck to you!
Q&A Library Searching Tips