This wish is a bit dangerous, but with proper cautions I believe it is doable for a reasonable healthy mid-level melee PC.
More specifically, I think you should be able to do this reasonable safely before doing the tower.
Things that help greatly in surviving this dangerous act are speed, HP and DV. Have as much of those
as you can. Max out toughness with morgia before you attempt this and dual wield shields!
You also need something else: a wand of door creation with at least 7 charges.
Step 1: before you enter the temple, plug your ears in advance.
Step 2: equip two shields, set tactics to coward!
Step 3: enter the temple and wish for a sheep
Step 4: Clear a pathway to the stairs down. Needless to say, avoid contact with the bugs!
Step 5: Descend and let the banshee clear the entry chamber.
Step 6: Use a wand of door creation to shut off the side chambers! Bugs can't open doors and
the banshee won't do it for them. This way, you can avoid most of the killer bugs and prevent the
banshee from gaining too many levels. The adom guidebook has a map of the level layout of the
bug temple, so here you can see which paths should be blocked.
Step 7: Head straight to the statue chamber, shutting of side chambers as you go.
Entering the statue chamber is the most risky phase of the whole operation. Have a potion of extra healing ready or be ready to pray. Once the statue chamber is clear, the banshee can be killed. On the way back, the path will be clear thanks to the created doors.