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. So for the example your gave:
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.