Packages dev got back to me and said there is no feature in the Apple installer format for prompting the user for a path. All files need to be set to a specific location.

However he said it might be possible using a plugin - written in Objective C or Swift.

@Dan-Korneff
@WillowWolf

Indeed.
Creating a custom filter is your best bet.

Digital SVFs are a particular topology which have limits to the shapes you can make with them. There are a few different methods to choose from to create digital filters with more flexible frequency responses.