Very long lines + php syntax

[alchemycs]

Hello,
I need to edit a php file with a couple very long lines (they are base64-encoded strings), I think the longest is over 300,000 characters.
I can edit the file perfectly fine as long as I don’t put a ‘<?php’ at the beginning of the file–as soon as I type ‘<?’ at the beginning, it starts to do the syntax highlighting, and then all of Sublime freezes (including other windows), and while I haven’t waited a super long time for it to come back, it seems to be pretty stuck.
This is on MacOS 10.8.4, running the latest v2 build 2221.
Any help would be greatly appreciated!
Thanks!