Yes.
1. Go to the first message and click "quote", just like you always do.
2. In a different tab or window, go to the second message and click "quote" just like you always do.
3. From the textbox labeled "Your message" of either quote, copy and paste the quote into the other textbox labeled "Your message" after (or before) the other quote.
When you copy/paste, be sure you include [ quote="nmoasis" ] and [ /quote ], without the spaces I have inserted here. You can delete any parts withing these two codes, but the codes must remain intact, and in order.
Each quote must stay separated from each other (no mixing or quote within a quote), unless you understand how the coding works.
If you were to quote me, I would not be alerted. And sorry, I see you already know a lot of this, but others won't.