This is an interesting question and, without manually modifying the compiled code, I'm not sure you can. But, since you asked for alternatives, there are a number of options:

• An encrypted data file that stores the key (you'll need to secure this)
• A local data store with encryption (need a data store installed in the app environment somewhere)
• A cloud key service accessible for each instance (AWS provides this)
• A K8s key store (if the apps are running in that environment)

You could simply read their public key and store it in a local file or something for use since it is "public" (i.e freely available and known).