RBK850 - Access Control and Guest Network

Hello!  Is there a way to use Access Control with the default set to "Block" but allow devices to join the Guest Network?  I want to prevent new devices from joining the primary Home network (hence the Block setting) but allow people who visit the house to use the Guest Network.  Right now it looks like Access Control is all or nothing (i.e. if I have it set to block, it won't even let people join the guest network).