With the Java keytool I can add multiple keys in the pkcs12 keystore:
keytool -genkeypair -alias foo -keyalg rsa -dname "CN=Foo, OU=..., O=..., L=..., C=..." -storetype pkcs12 -keystore keystore.p12
keytool -genkeypair -alias bar -keyalg rsa -dname "CN=Bar, OU=..., O=..., L=..., C=..." -storetype pkcs12 -keystore keystore.p12
How does one do this with openssl pkcs12?