You can actually change the verbs here to indicate reported speech; although you may change the meaning.
He said that had he gone to college, he would have done this.
This changes the conditional aspect of the statement slightly. It removes the implication of the lack of opportunity, so it transforms the meaning subtly. This says nothing, one way or the other, about whether this person faced barriers in obtaining an education.
He said that had he had the opportunity to go [to have gone] to college, he would
have done this.
And while this is closer to the original statement semantically, it's a tad awkward with had had.
He said that, had he the opportunity to go [to have gone] to college, he would have done this.
Had he had the opportunity and had he the opportunity are semantically equivalent to if he could have, but they might be more awkward.
And to go is much less awkward in my examples, but to have gone is also grammatical. I included have gone in brackets because it's obviously more reflective of the speech being attributed.
By the way, I'd suggest using would have done so for the reported speech. It's just a more common usage, but it's your choice.