that's ok
most giganteas ive seen have been in bark or a bark/sphagnum or seramis mix.
seen a few mounted on the big leaf orchids forum so it is possible even if the plant gets large
orchiata bark is supposed to last a long time but have problems with ph from what ive read.
don't know if any bodies tried growing one in chc though as some people says it lasts a long time.
the only other media is leca or a similar non organic media, think ive seen a gigantea grown in leca (not semi hydro) before.