There is a difference between acute dosing (once or just a couple of doses), and the repeated doses that post op patients get. The 8-10 mg is good for the first, while 2 mg q2 hrs prn is a nice starting point for the second (with hold parameters, and adjusted for age/weight). That is a whole different topic, though.
As for the seekers I adopt a few different strategies.
For the person who is a known substance abuser who has an identifiable reason for severe pain (trauma patients with real injuries, infected folks who get a big debridement), I discuss with them at the first possible moment that they are going to have pain and it is going to be difficult to control due to their abuse. I let them know that I will be trying a variety of methods to control their pain and they need to be patient since it may take some time until I find a good combination. I tell them the deal is that as long as they are cooperative with anything I try on them, that I will continue adjusting things until they get good control. Then I use a combination of meds. Usually this works out pretty well and they end up on stuff that isn't that much more than someone else in their condition (and is almost always po only)
For the ones that don't admit to using but are obvious about things (asking for IV benadryl despite taking po, asking for IV phenergan but not showing any signs of nausea, claiming 10/10 acute pain with no change in vitals and sitting there chilling when they don't know they are being observed, refusing to even try alternate medications, listing multiple "allergies" to pain meds) I base it on what I am seeing them for. If I think they are exaggerating pain they actually have, I will give them po meds (again I like a combo) and let them know that there is no medical reason to give them IV stuff. Often times this will help you get them out of the hospital, but all it takes is one person to give in to extend their stay. If there is no good reason for them to have pain, and they are being jerks, I will document very well and discharge them.
For the ones that I am not sure of (asking for certain meds because they know it has worked for them before-but willing to try other stuff first if I say so, claiming much more pain that would typically be seen with their injury/illness-but looking like it is legit even when you hide and observe, those with a chronic pain history that isn't something readily verified on imaging/records I have that I am seeing for something acute) I may start with some heavy hitting meds, but I still try to build a nice po regimen for them. A lot of times I may be satisfying a skilled seeker, but I know that not everyone has the same responses to pain (I for one require what could be considered huge doses of pain meds post op). At least that seeker will be pleasant, cooperative, and nondisruptive on future visits.