I recall an article, possibly in one of the April (spoof) editions of Computer Language magazine, outlining a method of adding GOTO to Forth. Probably considerably easier in principle - a buffer containing unresolved jumps, a support function to check the buffer and fill in the actual BRANCH addresses, and a couple of immediate words GOTO and LABEL to populate the buffer and call the support function. So provided your buffer data structure was clever enough and your GOTOs always matched a LABEL somewhere or other, it would handle forward and backward jumps easily. Evil, evil, evil.