Larry--
Interesting question. I think I'd re-work it a bit for use as an injection. Heres what I'd try:
In a small pot over very low heat warm the oil. Crush or chop 4 of the cloves of garlic (no need to peel) and crush or chop all the olives and add to the oil as well. Mince the remaining 2 cloves of garlic and reserve in a small bowl.
Mince the rosemary and add about 3/4 of it to the oil; reserve the remainder in the bowl with the garlic. Remove the zest of 3/4 of the lemon with a pairing knife in striips, avoiding the white pith (use your knife to trim off any pith from the zest). Twist the zest strips a little, over the pot, then drop them in. Remove the rest of the lemon's zest with a rasp or fine grater and reserve in the bowl with the garlic.
Add some freshly ground pepper to the bowl and a few crushed peppercorns to the pot.
Add 3 T oil to the bowl plus a good pinch of salt, mix well; reserve.
Stir the pot with the oil periodically. Do not allow the heat to get too high--you're not looking for even a slight sizzle. When about 15 min has passed remove the pan from the heat and allow the contents to cool in the pan.
Meanwhile: Pour the little bottle of gin (or the equivalent amount from the bottle on your bar) into a glass or cup.
Put a medium bowl on the counter and put the 2 T of olive brine in it.
Heat a small saute pan on low heat for a minute. If you have a gas stove: Pull the pan toward you so that it only rests half on the burner. Raise the heat to high. Being careful not to splash the gin, pour it all at once into the pan, then tip the pan away from you by lifting the pan's handle. With the pan on half the burner tipped toward the flame, the flame will ignite the alcohol vapors. When this happens, return the pan to flat on the full burner, reduce the heat to med-low and add the vermouth. Stir, allow to reach a simmer, then dump into the bowl with the olive brine and allow to cool. If you have an electric stove warm the pan on low then light a long match. Add the gin to the pan all at once, tip the pan away from you slightly, then light the gin collected on the other side of the pan. After ignition, return the pan to flat, increase the heat to med-low and add the vermouth. Stir, allow to reach a simmer, then dump into the bowl with the olive brine and allow to cool.
When the pan with the oil is cool strain it into the bowl with the gin, mix well, add some salt, fill your injecting needle, inject the lamb.
When ready to cook, bring the lamb to room temp, dry it, salt it lightly, then rub the garlic-oil-zest mixture you reserved earlier all over it. Cook.
I realize this is lengthy but I am writing stream-of-thought and not editing as I go. If you re-read it, though, you'll see that what I am suggesting is rather easy and quick--not drawn out or difficult as the length of the post would suggest.
If you try it let me know how it goes.