Currently, Strata does not have a CSV/INI loader for conventions like this. Thus, the simplest approach is to create a class that defines the conventions using Java code, just like
StandardTermDepositConventions (a package scoped class). You then add
com.you.product.deposit.type.YourTermDepositConventions = constants
to cause the class of constants to be loaded.
If you want to go further and write a CSV loader, you can. See
IborIndexCsvLookup for an example of how to write it. If you did that, then you would use a provider of "instance" as you suggest.
I also wanted to draw your attention to how our community driven support operates. If you feel that you are moving beyond initial setup and would like more formal support with service levels, then please contact us!