Using C-lightning RPC interface you can avoid specifying optional parameters, just by not specifying them. Using the console in Spark wallet shouldn't be different.

You can refer to a specific optional argument by its name while omitting the others by using the [`-k` command line option of `lightning-cli`][1]. So for the example your gave:
```bash
lightning-cli -k getroute id=024...a67 msatoshi=1000000sat riskfactor=10 exclude='["564334x877x1/0","564195x1292x0/1"]'
```

I don't know if Spark provides a way to refer to options by their name. You can always just specify the default of the options [as documented][2].


  [1]: https://lightning.readthedocs.io/lightning-cli.1.html#options
  [2]: https://lightning.readthedocs.io/lightning-getroute.7.html