It depends on how the student conceptualises multiplication. First, find that out. Then design an approach that uses it.
For example, if they think of multiplication as repeated addition, then you might try examples like:
$3\times(4+5)=(4+5)+(4+5)+(4+5)=(4+4+4)+(5+5+5)=(3\times 4)+(3\times 5)$
This approach gets messy trying to multiply out more than one bracket, so has to be taken slowly. Always do the brackets one at a time with this approach.
If they think of it as counting objects arranged in a rectangle, set out some objects on the table, or draw some pictures. How many red diamonds are there here? How does this picture represent the statement: $3\times(4+5)=3\times 4+3\times 5$?
Counting objects arranged in a rectangle is visually intuitive, which helps a lot, and makes an easy starting point to move on to interpreting it as an area. I personally think it's an easier approach than rearranging symbols as above. But the important thing is to find out where they are now, and then chart a course from there to where you want to go.
Also, start with concrete examples. Then illustrate the concept with pictures and diagrams. Finally, present the abstract/symbolic, once the basic intuition is there for it to connect to. "Multiplying out brackets" is the symbolic/abstract end stage. If they have been only shown the symbolic manipulation, that would explain why they have no intuitive grasp of why following the procedure works, and you won't get far without going back and introducing the supporting concepts.
If they haven't come across the area analogy, then I agree it is going to make it more difficult to introduce it right in the middle of explaining multiplying out brackets. But this ought to be telling you that you're trying to do things too fast, and out of order. Don't even think about teaching 'multiplying out brackets' until you have first taught 'multiplying', with an intuitive, visual analogy like areas or counting in rectangles or fixed-size boxes. (Like 'Widgets come in boxes of three. If we have four boxes and add five more boxes, how many widgets?') Then when you teach each abstract method, you have a visual/intuitive picture to link it back to.
If you want to use several such analogies/pictures, then introduce them all up front when teaching what multiplication is. Then later, when you run into difficulties with one approach, you have alternatives to fall back on, and you don't have to be introducing new topics in the middle of an explanation.