As sprite moves up, more jump pads appear on screen - ios

Question

I am trying to make a Doodle Jump-like game. I want to make it so that as a sprite, my main character, moves above a certain Y point, more pads to jump on appear, giving it the illusion that it is jumping higher and higher.
How would I go about coding this? Any examples would be nice. I am using SpriteKit in Xcode 7.
Here is my code so far:
import SpriteKit
import Foundation
class GameScene: SKScene {
var mainSprite = SKSpriteNode()
var wallPair = SKNode()
var ground = SKSpriteNode()
var moveAndRemove = SKAction()
override func didMoveToView(view: SKView) {
/* Setup your scene here */
mainSprite.size = CGSize(width: 30, height: 30)
mainSprite.color = SKColor.redColor();
mainSprite.position = CGPoint(x: self.frame.width / 2, y: self.frame.height / 2 - 100)
self.addChild(mainSprite)
ground.size = CGSize(width: self.frame.width, height: 300)
ground.color = SKColor.brownColor()
ground.position = CGPoint(x: self.frame.width / 2, y: 0)
self.addChild(ground)
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
/* Called when a touch begins */
createWallMap()
for touch in touches {
let location = touch.locationInNode(self)
}
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
}
func createWalls(height: CGFloat) {
wallPair = SKNode()
wallPair.name = "wallPair"
let rightWall = SKSpriteNode(imageNamed: "LeftWall.png") // I know it is opposite. Named the image wrong
let leftWall = SKSpriteNode(imageNamed: "RightWall.png")
rightWall.setScale(0.9)
leftWall.setScale(0.9)
rightWall.color = SKColor.redColor()
leftWall.color = SKColor.blueColor()
rightWall.position = CGPoint(x: self.frame.width / 2 + 340, y: height)
leftWall.position = CGPoint(x: self.frame.width / 2 - 340, y: height)
wallPair.addChild(rightWall)
wallPair.addChild(leftWall)
let randomPosition = CGFloat.random(min: -140, max: 140)
wallPair.position.x = wallPair.position.x + randomPosition
//wallPair.runAction(moveAndRemove)
self.addChild(wallPair)
}