Sorry -
The point of re-potting is to allow your roots to fill the new bigger area. Bigger root ball = bigger plant.
If you stick one pot into another, it's not going to allow the roots to fill the new container because the roots would still be contained in the first pot mainly.
You will get some roots that will grow out the bottom drain holes and into the new pot... but not enough to bother.
Give it a try if you want to do that, but honestly, you're not going to hurt the plant any more than letting it get rootbound than the mild stress of a transplant.
just be gentle with it.
I put my hand over top of the pot and slowly tip it over so that the mainstem is supported with my hand. You really only have to tip it enough so the hydrotron will come out of the pot.. not like right upside down or anything. If you have a nice ball of roots clinging to hydrotron.. that's good.
Put a base of hydrotron in the new pot and set the plant in the middle. While holding the plant in place take handfuls of hydrotron and fill around the plant.. don't pack it in or anything.. just let it fall in.
But you do what you want. It's a learning thing.. sometimes a person will only learn if they try things themselves (I'm like that personally).
Besides - you will see the results of doing one thing vs another and find what you like to do with them best.
Happy growing and good luck with everything