I have D rings on the sleeves of my suit with the arm restraints on them all of the time. I usually have a crew guy hook everything up because once the HANS tethers are attached I can't see down to do the belts. I also wear the arm restraints fairly short with just enough slack that I can get to the belt latch (and the fuel shut off, brake handle etc). I put the helmet on before I get in the car so that the built in head sock can be tucked under the suit before I zip the jacket up.
If you can't hook the arm restraints to the lap portion of the belt why not put them on the shoulder strap tangs? We did that in the fuel car because the leg straps of the 7 point harness were on the lap belt tangs.
Roo