[syslinux] constants and line continuation

[Warren Block]

If these are FAQ entries, sorry, I searched but did not find. 
Maybe the wrong terms.

Is there a way to define a constant value in a pxelinux.cfg/default 
file?

   httphost=192.168.1.1
   ...
   append fetch=http://${httphost}/...


Line continuations: it would be slick if multiple append statements 
could be used in a single menu entry, breaking up those four-screen-wide 
lines.  Tried that, and backslashes, but no.

Thanks!