Stretching. LOTS of stretching.
So, gradually going from small items to something as wide as a pylon. I'm only mildly exaggerating there. Some of the larger toys are truly unnatural in girth.
The downside? Loss of sphincter control. Prolapses. Possible incontinence because you have trouble keeping things in.
But hey, you're a fun addition to the fetish party, and can fit 2 arms up your butt. So, weigh the benefits.