The & special character is not supported?
Here is an example:
# delete duplicate, nonconsecutive lines from a file
sed -n 'G; s/\n/&&/; /^\([ -~]*\n\).*\n\1/d; s/\n//; h; P'
Here is a description of what it's supposed to do:
[2addr]s/regular _expression_/replacement/flags
Substitute the replacement string for instances of the regular _expression_ in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the RE and the replacement. Within the RE and the replacement, the RE delimiter itself can be used as a literal character if it is preceded by a backslash. An ampersand (&) appearing in the replacement will be replaced by the string matching the RE. The special meaning of "&" in this context can be suppressed by preceding it by backslash.
above reference found at: http://www.opengroup.org/onlinepubs/7908799/xcu/sed.html