With most other client libraries, objects are automatically serialized when being stored and retrieved from the system. This client library should have similar functionality.
For example, the Java spymemcached client library reserves the flags field for itself, and will set flags to indicate the datatype. One datatype is a serialized Java object.
One good option would also be to allow serialization into JSON, since there is good, built in support for JSON since 2.6 (I believe).