In principle, it's no problem, once you know what you are doing. I think "Honorable_Ensign" (hope I got the name right) was working on that. I've been helping him out every now and then but couldn't really do much as long as I didn't have my files at hand for reference. Also, I want to post the next chapter in my
sequence modding tutorial soon which will address some issues relevant to this.
The thing is, the MEHEM memorial is a modified version of the synthesis memorial. Getting it to be loaded after the destroy ending means changing the way the game streams levels into memory. That's what the next chapter of my tutorial will be about.
Of course, while the MEHEM memorial can be run while preserving the star kid, there is no way at the moment to preserve the synthesis ending so your choices would already be diminished (or you have to live with a glitched synthesis ending).
In any case, I'd suggest if you are interested in those kinds of modding questions, we should head over to the ME3Explorer forums. Problem is that you can get into specifics very quickly and at that point, it tends to get rather uninteresting for those not into modding the game. Also, there are more people over there that may be able to help out with questions.