Originally Posted by
tropikey
Thank you both very much for great advice!
As for now, we have Miles&More reward tickets only to LAX. Now I see that UA flight will be good way to get to LAS.
The only thing I need to do now is to convince Miles&More agents to add LAX - LAS leg to our itinerary. In case it won't be possible (even after using a "HUACA" method

), I'll simply buy 2 regular tickets, as prices for this connection are very reasonable.
[MENTION=19839]SS255[/MENTION]: thank you too

If you're unable to add the segment at no charge to current award, you might do a search for other 1-way, nonstop options from LAX-LAS that won't involve an 8-hour layover.
As an example, Southwest Airlines is a low-cost carrier (but not terrible) and they offer inexpensive, frequent service between LAX and LAS. You'll have to walk a bit and re-check your bag (and there's no lounge), but if you don't want to hang around the airport, they can probably get you out and on your way a lot quicker.