4.1 jelly bean - Install CA without having to activate screen lock

I have a Nexus 7 (Android 4.1.1) and I want to add a CA (Certificate Authority) to my device to use it for the ssl-connection to my mail server. The CA is self-signed. The Certificate does only contain the public key of the CA (of course!).

I also want to keep my screenlock disabled because on a tablet not leaving my house it does not make sense to have a screen lock.

Now the problem arises: Whenever I want to import the CA, Android wants me to change my screenlock to digits/password which I want to avoid.

Can this behaviour somehow be prevented? There is nothing security critical at a public key of a CA.

I know that when the phone is rooted one can add a CA, but I want to avoid rooting my phone.