With the C-lightning RPC interface, you can avoid specifying optional parameters, just by not specifying them. Using the Spark wallet console shouldn’t be any different.
You can refer to a particular optional argument by its name while omitting others with
-k Command line option from
lightning-cli. So for the example you 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 select only the default options as documented.