Não dá. Pelo menos não com os ajustes padrões. O que você pode fazer é usar o atalho Command + Option + D para ativar a ocultação momentaneamente e usar o mesmo atalho para desativá-la.
Eu não utilizo mas veja aqui o que encontrei:
Internet Security Barrier X6 for Mac - http://www.intego.com/internet-security-barrier/
Personal Antispam 10.6 Features
Filters e-mail and weeds out spam, placing it in a Spam folder
Filters spam with Bayesian analysis
Filters spam by address, message content, layout and more
Filters spam with a whitelist of users' contacts
Filters spam by developing a blacklist of spammers' addresses
Filters spam by top-level domain; users can exclude specific domains, such as .ru, .cn, .biz and more
Filters messages with incorrect encoding and identifiers
Filters phishing e-mails
Filters attachments for common file names
Trusts contacts in user's Address Book
Trusts ISP's spam headers
Learns from the spam users receive
Learns from legitimate e-mails
Does not slow down e-mail programs
Regular updates help fight spam as new types appear
http://www.intego.com/manuals/en/pas/images/pa-en-3-029.jpg
http://www.intego.com/manuals/en/pas/images/pa-en-3-024.jpg
http://www.intego.com/manuals/en/pas/images/pa-en-2-001.jpg
http://www.intego.com/manuals/en/pas/images/pa-en-3-012.jpg
fora esse tem outros conforme lista neste site: http://www.macupdate.com/find/mac/%2bspam/license
Depois informa o que achou.
Abraço.