We often used angles on each face of the opening, bolted through, with a plate welded below.  The angles would bear on the brick on either side of the opening.  It's not a pretty fix but gets the job done.

A temporary support can be provided by dimensioned lumber or steel channels that are temporarily bolted through the wall and the brick below removed and a lintel installed.

I have a standard detail that I use for these situations which incorporates the temporary works.

for lightly loaded walls use 8mm plate needles inserted through mortar joints with props at each end (check the capacity), otherwise use SHS or similar needles as required into pockets formed throught the walls.

under the needles insert a channel under each side of the wall . Bear on plate at each end onto brick and weld to needles above then cut off excess needle lengths and then encase in plasterboard/concrete as necessary for fire rating.

The architect is generally happier with this than angles either side as it maintains wall width and finishes.