As someone who works in a hotel as a front office supervisor, it took me a while to figure out a way which works well for me with all the standing etc too. so here are a few things i have learnt. which may or may not help. (but i hope they do)
Shoes- what shoes are you wearing? I found that whilst standing for a length of time a shoe with a small heel not only looks better, but helped my posture which in turn helped to stave off the back pain a little too (I also have a twisted spine)
Taking painkillers at the correct time- You will know better than i do how long it takes for you pain killers to hit your system. mine is twenty minutes so i take it twenty minutes before my shift and then every ////
heat- when i found these i was in heaven. they are a little expensive but wow, do they ever help. They are super skinny so no one will ever know you are wearing it, [and despite it saying 8hrs relief, they can lst up to sixteen http://www.thermacare.com/products-back-hip.aspx
Clicks - i rave about these. there not to expensive and they can be used over and over again. these might be useful. I use mine on a break on various sore area's jsut to give me a boost http://www.heatinaclick.com/tabid/580/l ... fault.aspx
Keep on moving- if you find the standing mroe difficult than moving, then keep moving. Walk around the resturant, keeping a eye on things but also will distract y ou from the pain. the more you do the less your pain will become as your mind will start to focus on other things.
Talk to your boss- sounds strange, but i struggled on without telling anyone for ages but i fond nothing but a ton of support from everyone at work. at quiete times i ould sit and do admin work so that i could give my hips a litte rest. This could work for you, you could polish silver sitting in the back (or similar!)
Try splinting your knee. there are a great range of splints out there. its always best to discuss with a OT ot doctor but it might be worth looking into.
I hope this helps, but feel free to contact me if you would like any more tips i find!
best of luck, lots of hugs
ZoeMod edit - dosage information removed, please read the site rules.