I've never done this before and I'm not 100% sure if it can be done. But there probably are ways if you're clever enough. So here's what I would try if I were in your position:
1. Check if there's a way to dump it with Odin. You can google around to see if it's possible but I'm pretty sure it's a feature in Odin (Whether our phone supports it is another story). You would have to boot into download mode, (vol down + home + power when powering on) and then follow whatever directions you find for dumping a rom. Just make sure you don't flash anything to your device. And make sure you know what you're doing with Odin because it can brick your phone if you push the wrong buttons.
2. The other way to do it is to dump your partition contents with the dd command (I would do it through an adb shell). This would require you to have root. I'm not sure of how to get root without modifying your ROM (kind of defeats the purpose of what you're trying to do if we have to change the ROM) but there are usually ways to get a temp root. Not sure how to do it on our phone but maybe someone else can help you with that part. Or maybe do some googling. The dd part I've at least done for the boot partition. Basically what you want to do is open an adb shell and run:
"ls -l /dev/block/platform/msm_sdcc.1/by-name/"
This will give you a list of all the partition name symlinks and show you the block devices they point to. For example, when I was getting boot.img I found that the "boot" symlink pointed to "/dev/block/mmcblk0p7". Find all the partitions you want to image in this list and figure out which block devices they point to.
The next part is to figure out how big each of the partitions is. You can find this in /proc/partitions. So from your adb shell you would run:
This will print out all of your flash block devices (look at the ones you were interested in from above). The 3rd column in this list will be the # of blocks in the partition. I believe the block size is 1k (1024 bytes). For example, my boot partition was 10240 blocks which comes out to 10 Megs, which sounds about right. The 1k assumption also agrees with the total device flash size, which is 7634944 blocks (mmcblk0) which is just under the 8GB they say the phone has. So I'm pretty confident about the block size.
So now we're at the part where things get a little hairy. I'm assuming you've found some way to get root in your adb shell. Be very careful with these dd commands and if you don't know what you're doing, don't do it. You would want to run something like the following:
"dd if=/dev/block/<partition name> of=/storage/sdCard/<name of image file> bs=1024 count=<# of blocks for partition you found in /proc/partions>"
You would do this for each partition you want dumped.
Again, be careful if you decide to try and do any of this stuff (especially with the dd commands, if you mix up the in file and out file you can brick your device). But like I said this worked for me to get boot.img and I was able to extract it and get the kernel and ramdisk. Hope this helps and sorry I don't know more about getting you a temp root without modifying your ROM.