How to use of blinding nonces in `sign_psbt`

I'm trying to sign with `sign_psbt` a pset created with [this version of libwally](https://github.com/ElementsProject/libwally-core/tree/psbt_v2_merge) that contains inputs owned by a `2of2_no_recovery` account.
As per [documentation](https://gdk.readthedocs.io/en/release_0.0.55/gdk-json/#sign-psbt-details), I have to pass a list of `blinding_nonces` within the JSON object, but it's not clear to me how to calculate or retrieve these values.