The only way is similarly kludgey - use the raw API (same as tctl uses). You can use the raw gRPC operator service call add_search_attributes directly. Here’s how we do the same thing you’re wanting in our SDK tests. Also by default search attribute addition may be eventually consistent, so you’ll need to pass a Temporalite option like this.
FYI, with the next server release we will likely change start_local to use Temporal CLI instead (see this issue) so any temporalite_ params will not work (they are marked experimental).