Is there an accessory product for dildos/vibs that would create a flange mount (universal sizing) similar to a Buttplug?

Honestly my gf and i love to walk around with BP's inside us...we will even sit down and just go about out business with them. We want to know if they make some type of accessory that would tighten around the base of a dildo / vibrator creating a flange so the toy doesnt slip inside.

The only thing that ive seen that could work is possibly using a 'knee harness' as a makeshift, but was hoping there is something more rigid.

Thanks!