MultiVI size factor for multiple modalities

In the methods from the MultiVI paper, both the expression and accessibility distributions contain ℓc - a term that captures cell-specific biases. In scvi.model.MULTIVI.setup_anndata, I believe setting size_factor_key overrides the estimated library size for expression.

Is there an equivalent parameter or a workaround for accessibility? I would like to be able to manually specify the library size for both modalities.