how to make a sling for a reflux wedge

[Cappy]

My baby has reflux and had been sleeping on a cocoonababy with some success. He's gonna outgrow it in coming weeks and I've bought a reflux wedge but the angle looks ridiculous although is what is recommended for baby reflux. I'll need to strap him in in some way. You can buy slings but they're expensive and only work for narrow weight ranges so one would need to replace them often. I've read about some arrangement of a rolled up towel and a pillowcase which people have come across on paediatric wards and which are used to position bsbies on medical grade reflux wedges. I can't for the life of me picture how the towel/pillowcase comno works. Maybe I'm being a dodo but if anyone knows how to make these homemade slings I'd be very grateful fir a step-by-step description of better still a photo,
thank you

In SCBU they roll up a towel, tight and coil it into a nest position, them put the nest into a pillow case and then position the nest on the wedge and put the baby in the nest. The nest needs to be in a horseshoe shape with the top of the horseshoe shape at the top of the wedge.

Only really works for little babies though that don't have the ability to roll etc.