Mike. It is a James Wong recipe, but with a bit of manipulation, he says to heat the lemon balm in three batches, which I did the first time, can't see it made a lot of difference and it was a real faff and you lost most of the oils from the bit's you couldn't quite wring out of the leaves. If you want some lemon balm, let me know I have a massive clump of it, and just got some variagated stuff that I've rooted from a cutting.

Elsa, You could just use something like almond oil, or even all olive oil, it would still work, the wheatgerm oil is supposed to have special properties but it is expensive and many recipes agree you can substitute other oils for it with little difference.