I just realised that provided you don't need to resize any partitions you can actually do it on the Mac.
WARNING Make doubly sure that you don't accidentally write in the wrong place.
The following script I wrote to rearrange Ubuntu MATE partitions and you should be able to adapt this to copy your data.
NOTE All care BUT no responsibility, and you really need to understand partitioning!
#!/bin/bash
# script to create a Ubunutu MATE image with properly aligned partitions
# 2015-11-06
echo
#INPUT_IMG="ubuntu-mate-15.10-desktop-armhf-raspberry-pi-2.img"
INPUT_IMG="PiMate1510back20151106_small.img"
OUTPUT_IMG="ubuntu-mate-15.10.img"
# Partition details of input image
P1START=2048
P1SIZE=131072
P2START=133120
P2SIZE=7546880
# Partition details of output image
P1NEW=8192
P2NEW=139264
# End of user configuration
#let IMG_END=$P2NEW+$P2SIZE+140000
let IMG_END=$P2NEW+$P2SIZE
echo -e $P1START - $P1NEW $P1SIZE
echo -e $P2START - $P2NEW $P2SIZE
echo -e $IMG_END
# Create an empty image file
dd if=/dev/zero of=$OUTPUT_IMG count=$IMG_END
# Create partitions
echo -e "
e 1
0C
n
$P1NEW
$P1SIZE
e 2
83
n
$P2NEW
$P2SIZE
quit" | fdisk -e $OUTPUT_IMG
echo "Finished Create partitions"
# Copy partitions
dd if=$INPUT_IMG skip=$P1START of=$OUTPUT_IMG seek=$P1NEW count=$P1SIZE
dd if=$INPUT_IMG skip=$P2START of=$OUTPUT_IMG seek=$P2NEW count=$P2SIZE
#fdisk $OUTPUT_IMG