Actually, $N identifiers can have text appended to them, and in the case of appending } its better to use $N}
Code:
alias notice notice $1 {Private message to $1} $2-

Or (longer and more obscure)
Code:
alias notice notice $1 {Private message to $1 $+ $chr(125) $2-


This, {Private message to $1 $+ } $2-, won't work.