I'm not familiar with the E46 in particular, but I'd be surprised if there
is enough clearance to tap the hub from the rear without removing it first.
Though you might just succeed if you canibalise the tap. Even to the extent
of cutting it down to just a small stub, with a pair of flats for a spanner.

If you're very careful though, making sure the tap is absolutely square.
(use a small square or something fabricated to constantly check) you may be
able to pick the original thread up from the front.
That would be my first option.

Failing all those, a final option, without hub removal, would be to drill it
out and fit a 'Helicoil' thread insert. Make sure it is a genuine Armstrong
Helicoil. Not one of the many thread inserts made by other Co's, that IMO
are just nowhere near as good.
Mike.

And the rest.

Get a magnifying glass and have a close look.

Use suitable tools (e.g. wood chisel - sacrificed) to try and put the
original threads back in position.  Remove any that are mashed.

In principle you should then be able to use a tap (or a Hilti bolt the right
size) to refurbish the thread.  As the thread starts gradually on the tap
you should be able to get it started very easily and once going push any
bent squashed bits back into position (albeit a bit weaker).

If the tap jams (e.g. to trapped pieces of loose thread) remove it, remove
any impediments and start again.

Have another look and remove any loose bits of thread etc.

Finally refit your bolt - but line it up properly first this time!

Unless the threaded section is very thin your should be OK.

And the rest.

Get a magnifying glass and have a close look.

Use suitable tools (e.g. wood chisel - sacrificed) to try and put the
original threads back in position.  Remove any that are mashed.

In principle you should then be able to use a tap (or a Hilti bolt the right
size) to refurbish the thread.  As the thread starts gradually on the tap
you should be able to get it started very easily and once going push any
bent squashed bits back into position (albet a bit weaker).

If the tap jams (e.g. to trapped pieces of loose thread) remove it, remove
any impedements and start again.

Have another look and remove any loose bits of thread etc.

Finally refit your bolt - but line it up properly first this time!

Unless the threaded section is very thin your should be OK.

And the rest.

Get a magnifying glass and have a close look.

Use suitable tools (e.g. wood chisel - sacrificed) to try and put the
original threads back in position.  Remove any that are mashed.

In principle you should then be able to use a tap (or a Hilti bolt the right
size) to refurbish the thread.  As the thread starts gradually on the tap
you should be able to get it started very easily and once going push any
bent squashed bits back into position (albeit a bit weaker).

If the tap jams (e.g. to trapped pieces of loose thread) remove it, remove
any impediments and start again.

Have another look and remove any loose bits of thread etc.

Finally refit your bolt - but line it up properly first this time!

Unless the threaded section is very thin your should be OK.

Usually, you can simply use a tap to repair the threads. The tap is tapered,
so it should thread past the screw-up area and become properly aligned so
that the thread cutting portion of the tap can do its thing.

Front or Rear??

Thanks very much for the advice given in response to my original post.  
I considered the various suggestions and concluded that the easiest and
cheapest thing to try first was to try to re-tap the damaged threads, so
out I went to get the proper tap (12mm x 1.50)this morning. Cost $5.

Luckily, I was right in my initial impression that very little of the
thread had been damaged once I had done a magnified inspection of the
hole, so I offered-up the tap to the hole and started to turn, applying
firm pressure, and the thread recut easily and quickly.

Lug-bolt reinstalled.

Thanks again for the advice!

Jon