|Unless you are very familiar with encryption and a competent programmer you cannot. You are stuck with what is provisioned, all or nothing.|
Besides, partial encryption is a hackers paradise, it is as bad as no encryption at all. The unencrypted data will provide clues as to what is in the encrypted data and make the hackers job that much easier.
That is how the Enigma codes got cracked in WWII. Operators sending unencrypted test messages immediately before sending an encrypted message.