No, not possible. You would need to submit a brand new application under the H&C program. A spousal sponsorship application cannot be converted to an H&C application. The spousal sponsorship application is completely dependent on having your spouse sponsor you until PR is approved.
If you have other H&C grounds, you need to submit a new H&C application directly through this program. Unfortunately this means that processing times will restart from scratch. That is the only option if your spouse withdraws their sponsorship.
