I just found out that SN v2.0 Works With PFX Files and you can create private key (self signed digital certificate) .PFX files (PKCS#12) in Microsoft Visual Studio.NET 2005 from the same place you create .SNK files.
“The logic here is that a self signed certificate stored in a PFX file is the moral equivalent of an SNK key, except that it gives you the added benefit of storing your key in encrypted form rather than in the SNK’s plain text format.”
Some limitations mentioned in the blog post:
“SN will not accept a PFX file which contains multiple certificates”
“SN will not allow you to redirect standard input and load the password from a pipe”
“SN will never attempt to read a certificate with a NULL password” – “the PFX file must have a password, even if that password is blank”