I personally wouldn't recommend using a ratchet strap. Even if the strap has the correct working load rating to hold the strength of the spring.
First, the spring already has a certain amount of tension on it... before you put the strap on it.
As you stretch it with the ratchet strap to remove it, you will add more tension to it.
Ratchet straps don't "un-ratchet" slowly... They release all of the tension at once... just like your garage door springs when they snap/break, or if you let go of the rods used to slowly unwind them. You cannot control the release pressure when you need to loosen the strap.
If you look at the photo of the tool, already supplied, and are handy, you should be able to make you own.
Another option would be to find and buy or borrow one from someone.
As mentioned, anytime you are working with springs like this, make sure you put plenty of padding around the area and wear proper safety equipment (gloves, safety glasses, etc.
Safety first... we want to see both you and your car out and about, healthy and happy.