I generally have the rule that I will use 1/4th of what I'm prescribed but only as needed. The rest sit... or something. I'm scripted 80mg oxymorphone, I take 5-10mg daily before bed (nasally, however).
It is easily the hardest drug I have had self-control issues and I can already see addiction in my future... I'm trying to balance risk/reward and keep it low, but tolerance I am sure will fuck me.
Fortunately there is almost no chance I will be forced to cold turkey quit as I am a pain center patient at many places and getting any opioid isn't really a problem with my level of pain and documentation so long as I can piss clean (minus opiates).
/derail
On topic: that is the reason I use these synthetics, though they have proven to have tremendous other value that cannabis does not: ie: easy transportability, easy to smoke anywhere, insanely easy to dose orally, and price is almost a none-factor compared to what I was spending on cannabis (1k a month average, though last summer I easily went through 8 grand - not to say I didn't recoup some, but still.). They're also a lot of fun to make your own blends with, and mix with other synthetics to get an entirely new drug... Also, I rather enjoy that if I want, I can make a blend that will give me a ~45 minute high, or one that will give me a ~3 hour high (combo of win/018/250/073).
The downside is there is nearly no documentation on these drugs - and soon my favorites (018) will become standardedly tested for. The half life isn't nearly as painful as cannabis though, so that's still not a huge issue... I am more concerned with the rumor mill of bad things - but I've used heavily for 5 months now, or around there, and suffered no ill side effects... In fact, JWH instead of weed has boosted my general attitude as well as willingness to stay clean & on top of my work - probably due to it's short duration.