You can't be in receipt of IFR departure instructions, for a start.
AFISOs can, and very often do, read IFR clearances issued by London Control.
You can take off from a farmer's strip IFR, fly 200 miles IFR, and land in VMC at another strip without ever mentioning it to anyone, whether by FPL, telephone or radio, providing you remain clear of regulated airspace.
And remember a few things before we have more expletives about such a trip:
IFR does not necessarily imply IMC
The need to fly IFR might be that you are flying at 500' below a 4000' cloud base in 30km vis (that's IMC!)
Even if you are fully IMC all the way (except the first 500' and the last 1500', say) you are statistically infinitely less likely to have a mid-air than someone else doing the same thing VFR on a gin-clear day.
Will