After some googlage, I came up with the following. Given a tarball and an installer script named ‘installer’, it will create a self-extracting bash script:

#!/bin/bash
#############################################################
# Self-extracting bash script creator
# By Dale Maggee
# Public Domain
#############################################################
#
# This script creates a self-extracting bash script
# containing a compressed payload.
# Optionally, it can also have the self-extractor run a
# script after extraction.
#
#############################################################
VERSION='0.1'

output_extract_script() {
#echoes the extraction script which goes at the top of our self-extractor
#arguments:
# $target - suggested destination directory (default: somewhere in /tmp)
# $installer - name of installer script to run after extract
# (if specified, $target is ignored and /tmp is used)

#NOTE: odd things in this function due to heredoc:
# - no indenting
# - things like $ and backticks need to be escaped to get into the destination script

cat <<EndOfHeader
#!/bin/bash
echo "Self-extracting bash script. By Dale Maggee."
target=\`mktemp -d /tmp/XXXXXXXXX\`
echo -n "Extracting to \$target..."

EndOfHeader

#here we put our conditional stuff for the extractor script.
#note: try to keep it minimal (use vars) so as to make it nice and clean.
if [ "$installer" != "" ]; then
#installer specified
echo 'INSTALLER="'$installer'"'
else
if [ "$target" != "" ]; then
echo '(temp dir: '$target')'
fi
fi

cat <<EndOfFooter

#do the extraction...
ARCHIVE=\`awk '/^---BEGIN TGZ DATA---/ {print NR + 1; exit 0; }' \$0\`

tail -n+\$ARCHIVE \$0 | tar xz -C \$target

echo -en ", Done.\nRunning Installer..."

CDIR=\`pwd\`
cd \$target
./installer

echo -en ", Done.\nRemoving temp dir..."
cd \$CDIR
rm -rf \$target
echo -e ", Done!\n\nAll Done!\n"

exit 0
---BEGIN TGZ DATA---
EndOfFooter
}

make_self_extractor() {

echo "Building Self Extractor: $2 from $1."

if [ -f "$3" ]; then
installer="$3"
echo " - Installer script: $installer"
fi

if [ "$4" != "" ]; then
target="$4"
echo " - Default target is: $target"
fi

src="$1"
dest="$2"
#check input...
if [ ! -f "$src" ]; then
echo "source: '$src' does not exist!"
exit 1
fi
if [ -f "$dest" ]; then
echo "'$dest' will be overwritten!"
fi

#ext=`echo $src|awk -F . '{print $NF}'`

#create the extraction script...
output_extract_script > $dest
cat $src >> $dest

chmod a+x $dest

echo "Done! Self-extracting script is: '$dest'"
}

show_usage() {
echo "Usage:"
echo -e "\t$0 src dest installer"

echo -en "\n\n"
}


############
# Main
############

if [ -z "$1" ] || [ -z "$2" ]; then
show_usage
exit 1
else
make_self_extractor $1 $2 $3
fi