I personally would take 400-600mg Tagamet, 16oz Grapefruit Juice, and 25-50mg Diphenhydramine about 45 minutes before you plan to take the OC. Then, 30 minutes prior, take 1-2 Tums to negate the acidity of the GFJ. This should potentiate the oxycodone nicely.
(Amounts of oxycodone listed are not necessarily what you need to take, but should give you an idea of the proportion between MOA's)
First, you should crush up, say, 20mg of OxyContin really, really well (first by smashing repeatedly, and then by chopping and dicing with a razor and/or sharp knife) and parachute it. You do this by putting the OC powder in the center of a square of toilet paper, and then twisting it up so that it's essentially "closed", putting it in the back of your mouth, and then swallowing it with a LOT of water so it doesn't get stuck in your throat. Parachuting increases surface-area, and means the stomach has to do less work breaking down the drug, so it will absorb better and faster. (Note: if not chopped well, you won't defeat the time-release and you won't feel nearly as much; it's really important to spend a lot of time really "working" on the pill)
Then, after about 15-20 minutes, I would take 10-15mg and crush/dice/slice it up super-fine (should be a powder-like consistency, not grainy), divide it into two lines, and snort one up each nostril. This will kick in quickly, reaching peak effects within 5-10 minutes as opposed to 25-30 minutes when parachuted (oral). This means that the two ROA's will kind of "coincide" with one another, and you'll get hit nice and hard, having the benefit of a long, smooth high from the oral use, as well as a quicker, "harder-hitting" peak from the intranasal use.
On top of it all, by using the potentiators listed above, you can increase the high by as much as 25% and increase the length by the same, if not more. I've had a good potentiation increase the length of time I was high from oral Roxicodone from 5 hours to 8. That's pretty significant, especially considering I used 80mg instead of my usual 100-120mg.