I've had some fairly decent results from my attempts to "synthesise" the spiced oils.  The end results look pretty similar to MarkJ's pictures shown earlier in this thread, a nice reddy goldy colour, tastes savoury with sweetness and spice underneath and smell fantastic.

Essentially I use the same method as making a stock for soup except with oil rather than water. Heating bits of vegetables and seasoning over a low temperature for a fairly long time.

I use a small bottle of oil and really just use what ever is at hand to flavour it. Some pepper, or even just the cores - if thats the word - from the pepper as these impart quite a bit of flavour,  some onion, a few green chillies, a couple cloves of garlic, bay leaves, pepper corns, cumin and coriander seeds, some coriander stalks etc and some spice mix to try to marry the flavour of the oil to that of the finished dish / base.  I'd say the closer the ingredients you use are to those in your base the closer the oil will taste to the oil you would reclaim from your base.

I then put it over a low heat for a good few hours to flavour - the longer the better, I'd say this is the most important aspect, the same as with stock - and then leave to cool and infuse further overnight.  I run it through a sieve or colander  to remove the whole spices, veg etc and then through a coffee filter to remove the sediment from the spice powders and pour it back in the bottle and keep it in the fridge.

I suppose its quite similar to making a base except with no other liquid, or any thing that will melt and turn in to a liquid, other than the oil meaning you can reclaim 100%.