One thing that some of the more hardcore games include is a virtual joystick. This is now available to you in the next build of iStencyl (b26) as a natively supported feature. You just need to use a block and provide 2 images to enable it.
Once you do, you then use 2 blocks - one for direction and one for magnitude, to do whatever you need to do.
I've attached a walkaround demo that demonstrates this all in action.
(THIS ONLY WORKS IN b26+, not the current build you have)