I should also add to my post above:
If I know that IFR might be a possibility, I will also tell our ops center:
IFR is a possibility, so I will either:
a. put on extra fuel before departing
b. drop off the med crew at the patient and go get fuel.
I have also been in the position where I have added fuel before departing and then found that the patient weighed so much that I could not take them with enough fuel to go IFR. Then I discuss with our ops folks items 1 and 2 from my post above.
Another option, and certainly not optimal, is to stop en route and put on more fuel with the patient on board, though not every program may allow this.