If you're happy to always have at least one blank line, you could define some spacer variables to use. Note that using a monospaced font lets you control the width much better:
@startsalt
!$pad40="<font:monospaced> </font>"
{+
This is a long
text in a textarea
$pad40
}
@endsalt
If you have lots of different widths, you could use a macro to generate a specific width spacing line on demand:
@startsalt
!function $pad($width)
!$spaces=""
!while %strlen($spaces) <= $width
!$spaces=$spaces+" "
!endwhile
!return "<font:monospaced>"+$spaces+"</font>"
!endfunction
{+
This is a long
text in a textarea
$pad(40)
}
@endsalt
Before I came up with that, I experimented with a macro to pad out strings to a set length, so I'll include that too. The advantage is that there's no need for a blank line. The disadvantage is that you either use monospaced font throughout or you use lose precise control over the width.
(click diagram for source)