Yes, that's possible. For this we need to adjust some settings on your side within your account and you also need a bit of extra software from us. If this has not yet been set up and you are interested in this, please email email@example.com. Once it's all set up, you can sign with a certificate setup in the following way:
You go to the transaction (or you create a new one) for which you want to set up a signer with a certificate. Then click "Settings" next to the signer.
You can then set this signer to sign with a personal certificate via "External authentication".