The lever back earrings that I use can be purchased disassembled or
can be disassembled for this reason. Try removing the rivet pin and
spring assembly and reassembling after you solder the base onto the
earring.
Short of lasering or arc welding the finding, you must disassemble
it to solder. Use a ball bur to remover the spread rivet on one side
at the lever and push the rivet out with a fine point center punch
or a dead bur thats been sanded to a point. remove the lever and
solder . Rerivet with 22ga., file it to a point if necessary to work
it through, 24ga will fit easily but is way too sloppy, the hinge
will drift too much.
ciao, gail