I have been working on a sight for the WRg21 rocket.
Just hold the bar slightly above the wings of the center bomber and shoot when the wingspan matches the width of the bar. This is set for the B-24 which has the largest wingspan, the B-17 and Lancaster are just about 10 feet narrower.
Just line up and approach like Krusty posted and you'll be close.
On a side note, I have a copy of the Fw190 A-8 Aircraft Handbook from rareaviation.com. This is an English translation of D.(Luft) T. 2190 A-8 issued September 1944 and effective July 1944. In section 8C Special weapons systems subsection D outlines the operation of the emergency release system.
There is an explosive bolt in the carrier strut that would sheer and the launch tube and the 4 bracing struts would fall from the aircraft leaving only the small single half of the carrier strut.
The first line of the section says "In an emergency".
So you close circuit breaker P1 and safety switch I complete the circuit. Then actuate toggle switch P801 marked (Absprengung Gerat 21") located on the right side of BR armament panel. P801 is held in the safe position by a spring loaded plate.
I was rereading "Half a Wing, Three Engines and a Prayer" by Brian D. O'Neill
Which covers the combat tour of a crew with the 303rd Bomb Group in the 8th
Air Force and the crew speaks of often being attacked by rockets. One thing I noticed was that most of the time they were talking about rocket attacks, they were not protected by escorting fighters.
So I can see that in real life the tubes were not ejected that often. However, the way Aces High is played (in the main arenas) bares little similarity to the actual events as well. So it would make sense to me that the option to jettison the tubes should be available in the game. But that's just my opinion.
Good luck with the sight it works in 109's, 190's and the 110. You just need to hold it a little higher in the 109 and 190's.