How can I ignore insignificant change during merge ?

[Jens Brejner <jens@kaabrejner.dk>]

I need to merge a branch, +100k changes. The vast majority of changes
are insignificant, because they only represent a screen position in
the editor, so these changes should never have been in git - but but
MadCap Flare already put them there.

The files in question are xml, and the difference can be exemplifed like this:

Original (when branches were created):
html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd"
MadCap:lastBlockDepth="5" MadCap:lastHeight="32"
MadCap:lastWidth="400"
Branch1:
html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd"
MadCap:lastBlockDepth="5" MadCap:lastHeight="24"
MadCap:lastWidth="500"
Branch2:
html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd"
MadCap:lastBlockDepth="5" MadCap:lastHeight="41"
MadCap:lastWidth="300"

How can git help me so files where the only difference matches
something like this regex:
/html xmlns:.* MadCap:lastHeight="\d+" MadCap:lastWidth="\d+"/

for the files that qualify, I want git to ignore the change, and
therefore the merge-conflict, and then just accept "my" file for the
merged changeset.

Any suggestions on how to I can have git help me with that ?

Best regards
Jens Brejner