If you know of all of the strategies in advance (i.e. at template definition time), you can have a simple enum on the wire and use that.
If you want a more open-ended set of options, you’ll need to invent your own mini-language and write an interpreter for it in Daml. It’s not very difficult (if you keep to an abstract syntax and skip over all the parsing stuff) for a simple arithmetic language. See this post for a more in-depth example.
Edit: This discussion may also be relevant.