Apply by doing:
	cd /usr/ports/infrastructure/mk
	patch -p0 < /path/to/lzma.diff

The ports Makefiles contain "EXTRACT_SUFX= .tar.lzma" which will
automatically pick up lzma as a build time dependency.

Index: bsd.port.mk
===================================================================
RCS file: /cvs/ports/infrastructure/mk/bsd.port.mk,v
retrieving revision 1.937
diff -u -r1.937 bsd.port.mk
--- bsd.port.mk	15 May 2008 10:09:29 -0000	1.937
+++ bsd.port.mk	16 May 2008 17:21:24 -0000
@@ -571,6 +571,7 @@
 TAR ?= /bin/tar
 UNZIP ?= unzip
 BZIP2 ?= bzip2
+LZMA  ?= lzma
 
 
 MAKE_ENV += EXTRA_SYS_MK_INCLUDES="<bsd.own.mk>"
@@ -1007,8 +1008,13 @@
 	(defined(PATCHFILES) && !empty(_PATCHFILES:M*.bz2))
 _USE_BZIP2 ?= Yes
 .endif
+.if !empty(EXTRACT_ONLY:M*.tar.lzma) || \
+	(defined(PATCHFILES) && !empty(_PATCHFILES:M*.lzma))
+_USE_LZMA ?= Yes
+.endif
 _USE_ZIP ?= No
 _USE_BZIP2 ?= No
+_USE_LZMA ?= No
 
 EXTRACT_CASES ?=
 
@@ -1025,6 +1031,11 @@
 EXTRACT_CASES += *.tar.bz2|*.tbz2) \
 	${BZIP2} -dc ${FULLDISTDIR}/$$archive | ${TAR} xf -;;
 .endif
+.if ${_USE_LZMA:L} != "no"
+BUILD_DEPENDS += :lzma-*:archivers/lzma
+EXTRACT_CASES += *.tar.lzma) \
+	${LZMA} -dc ${FULLDISTDIR}/$$archive | ${TAR} xf -;;
+.endif
 EXTRACT_CASES += *.tar) \
 	${TAR} xf ${FULLDISTDIR}/$$archive;;
 EXTRACT_CASES += *.shar.gz|*.shar.Z|*.sh.gz|*.sh.Z) \