What I mean is Ewell or Trimble taking the high ground before the end of the day. As Trimble thought of taking Cemetery Hill, weren't there any other divisions in the area that could have assisted them?
In order of least to most bloodied:
Anderson's division is being held in reserve by Lee, and would also take time to actually assemble and position for an attack even if not sent into bivouac.
Johnson is coming up but won't be in a position to engage for at least a couple hours.
Early's division has two brigades watching the flanks of Ewell's corps, which leaves the other two as the two brigades in question.
Rodes's division has suffered heavily and will be at least an hour most likely getting in position, even if orders are issued ASAP.
Pender's division is banged up but not
entirely unfit.
Heth's division is a wreck.
I agree with Ewell about the battle of Gettysburg (paraphrased: It took many mistakes to lose Gettysburg, and I made several of them.), but this is not one of them. Not unless Lee sends Anderson forward instead of holding his division in reserve.
So Ewell or Trimble taking the high ground requires that, at a minimum, in order to have any realistic chance - by the point Ewell can do more than throw Avery's (properly speaking, Hoke's) and Hays's brigades at the hill, the Federals have reinforcements very close too.