I was biking there a few weeks ago during working hours, and they had a marked detour going right through the middle of the construction area that day, right around the parking lot’s ticket booth, with heavy equipment working on both sides. One of the workers signaled to the driver operating near the detoured bike path to move out of the way, and waved me through when it was safe.
I think there have been different detours at different times. So far, I’ve always been able to get through, though I haven’t been there in at least a week.
If the usual route is completely blocked, you might try taking the sidewalk from the end of 26th street. Failing that, Google’s satellite view suggests that it might be possible to head all the way down 24th Street, turn right at the parking lot, and at the far northeast corner, take a narrow bridge over the railroad tracks to the trail. No idea if that’s even possible, much less safe, nowadays.