Q:

Sublime Text multiline comment with partial selection

Could I make multiline comment for partially selected lines with default Sublime Text adjusments?  
Select the text this way:

And press Ctrl+/ to comment from the beginning of the block to its end.

A:

I guess I found a kind of workaround.
It was inspired by the file Default.sublime-mousemap. There is an action which uses Right mouse key as modifier and expands the selection to the line boundaries:
{
  "button": "button1", "count": 1, "modifiers": ["button2"],
  "command": "expand_selection", "args": {"to": "line"},
  "press_command": "drag_select"
}

So the steps to perform the full line comment on partial selection:  

Create a macro and save as comment-add.sublime-macro to the Packages\User:
[
  {
    "args": 
    {
      "to": "line"
    },
    "command": "expand_selection", 
  },
  {
    "args":
    {
      "by": "characters",
      "extend": true,
      "forward": false
    },
    "command": "move"
  },
  {
    "args":
    {
      "block": false
    },
    "command": "toggle_comment"
  }
]

Add custom keyboard shortcut:  
{
    "keys": ["ctrl+shift+2"], 
    "command": "run_macro_file", 
    "args": {"file": "Packages/User/comment-add.sublime-macro"}
},

Select blocks with partial lines and use the shortcut to comments whole blocks.

