Define preferred position for line break

Is there any way, preferably using CSS, to define a preferred place for a line break under the condition that the whole text will not break into more than 2 lines?

Let’s say we have a sentence like this:

This is the rather lengthy main clause, but here's a sub clause.

I want to break the sentence at the comma.

But I do not want to have it break into a third line if there’s not enough horizontal space. In this case, my forced line break should just be ignored.

// wide screen (perfect):

| This is the rather lengthy main clause,                 |
| but here's a sub clause.                                |


// narrow screen (bad):

| This is the rather lengthy main  |
| clause,                          |
| but here's a sub clause.         |


// narrow screen (good):

| This is the rather lengthy main  |
| clause, but here's a sub clause. |

How would I go about this?