Pardon me for a potentially boneheaded clarification here, but restrained like "don't jostle around on the cot / keep your arms in on the stairs / don't hit the back door when we gun it?" Because if it's that, you can just get normal retracting-centrifugal-clutch-type or manually-tightening kind of seatbelts that have a carabiner on either end for which you should be able to find a home on the cot...(some even using the manual-tightening kind as their backboard strap.) Ambos in my neighborhood run everyone with one of these on their lap and one across the chest. Kids go in a car seat. If it's more for a "stop hitting me / I'm not Satan / put down that needle" purpose, we have soft restraints that go around the wrists and ankles, and a somewhat elaborate but still usable protocol for using them that might have some ideas for you... (For a particular laugh, check out the "verbal" restraint portion that precedes the "physical" and (medic-only) "chemical" restraints. Of course, most of those people we get that would need to be restrained that way come from a scene with the cops, and are going to ultimately stay in their hands at the hospital, so we go with the old reliable - handcuffs applied by (and under the liability of) a cop, who then rides in the back with us.