Short answer you can't sorry.
Long answer... Go to your G3HS ini and find the line that has the type of evolutions like: Level, level, trade, trade, item, item, level ... etc.
You can change them to I think 'Move","Map" and another one... read the documentation. When you choose the move in G3HS it sacrifices the 'level' slot for any move you pick.
The reason for this was so any move can be chosen, and any town and map can be chosen too! But it does sacrifice the level option. That also explains why holding an item cant also be used for a certain level.
I hope this helps, if you really want a way around it you need to make a custom ASM file for each pokemon. What you need to then do once the move check is performed...
say it evolves at level 32, you must load in R2 0x20 and then b levelcheckloc
it should work from there. But it is unique and only works for level 32 pokemon evolutions. Hope this helped