Luc,
You apply for the permit online if you are not in too much of a hurry. It took my application about two weeks to process (until I got my permits in the mail). If he needs the plant import permit (I think it is level "2") they will need to go to a local office.
Hope this helps,
Richard
EDIT I actually did it by mail rather than online, but it still took about two weeks. I had to go to the local office in person to be able to do some of the online permit applications. Also, here are the Maui Service Centers, they should be able to help
HOOLEHUA SERVICE CENTER
4101 MAUNALOA HIGHWAY (NEAR AIRPORT)
HOOLEHUA, HI 96729-0396
(808) 567-6868
(808) 567-9062 fax
KAUNAKAKAI SERVICE CENTER
KAHUA CENTER, 15 KAUNAKAKAI PL
KAUNAKAKAI, HI 96748
(808) 553-5321
(808) 533-3739 fax
KAHULUI SERVICE CENTER
77 HOOKELE STREET, SUITE 202
KAHULUI, HI 96732
(808) 871-5500
(808) 873-6184 fax