I see that wip/foomatic-filters-cups just does one thing:

  ln -sf ../../../bin/foomatic-rip ${PREFIX}/libexec/cups/filter

So maybe add to print/foomatic-filters/Makefile:

PKG_OPTIONS_VAR=        PKG_OPTIONS.foomatic_filters
PKG_SUPPORTED_OPTIONS=  cups
.include "../../mk/bsd.options.mk"
.if !empty(PKG_OPTIONS:Mcups)
PLIST_SUBST+=           USE_CUPS=
.include "../../print/cups/buildlink3.mk
.else
PLIST_SUBST+=           USE_CUPS="@comment "
.end


And in the post-install target add:
.if !empty(PKG_OPTIONS:Mcups)
 	${LN} -sf ${PREFIX}/bin/foomatic-rip ${PREFIX}/libexec/cups/filter
.endif

And in the PLIST add:
${USE_CUPS}libexec/cups/filter/foomatic-rip


The above is untested. But I think wip/foomatic-filters-cups package is 
probably un-needed.

  Jeremy C. Reed

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