I'm not sure this will work for you, but here's one possible solution for getting better performance:

1. Create a cache of entities via ent_create during game initialization (or during some idle time) from the server computer
2. Hide the entity (i.e. make it invisible)
3. Register the entity with MP_RegisterWED_Entity
4. Make the entity visible when you need it.

As you probably guessed, creating entities is an expensive process, especially when the entity has to be propagated to all the remote machines. I'll see what I can do to tweek this, but I'm not optimistic that I can make multiplayer entity creation significantly faster.