From Joseph E.A. Connell's book "Dublin in Rebellion" the list of men in the Boland's Mill Garrison includes Leo Fitzgerald.
Apart from his name being listed, there is little further information that I can find in the book.
Under Great Brunswick St. (now Pearse St.) it reads:
"Home of Leo and Billy Fitzgerald. The family's members were prominent Volunteers in the 3rd Battalion; raided for arms in February 1916. After the Rising, Seán McMahon, Quartermaster of the IRA/Volunteers, used their house as his HQ."
Dara.