How to get around or make PHP json_decode not alter my very large integer values?

So I'm using php 5.2.6 in a WAMP environment.

I'm trying to use the json_decode function to make a json string into an array. The JSON is coming from a REST API elsewhere so I have no control over formatting of the JSON string. Here is an example of one of the json strings I'm trying to use:

[{
    "webinarKey":795855906,
    "sessionKey":100000000041808257,
    "startTime":"2011-12-16T13:56:15Z",
    "endTime":"2011-12-16T14:48:37Z",
    "registrantsAttended":2
}]

I'm specifically after the sessionKey value here. PHP is treating the value as a float and I can't seem to do anything to retrieve the original value.

I've tried the following:

json_decode($json, true, 512, JSON_BIGINT_AS_STRING);
# This produces the following error because my php version isn't up to snuff and I
# can't upgrade to the version required
# Warning: json_decode() expects at most 2 parameters, 4 given

I've also tried this:

$json_obj = json_decode($json, true);
number_format($json_obj[0]["sessionKey"], 0, '.', '');
# This results in precision issues where the value was 100000000041808257
# but is number_formated out as 100000000041808256

As I said, upgrading to php 5.4 (where the 4 parameter json_decode call is supported) isn't an option. Please help!

Thanks!

Solution

Thanks @Scott Gottreu and @pospi.

The answer was in the last comment for the accepted answer on this question.

Use the preg_replace() function to surround all integer values with quotes.

json_decode(preg_replace('/("\w+"):(\d+)/', '\\1:"\\2"', $jsonString), true);

Actually after testing the above line it screws up JSON with floating point numbers in as values so to fix that issue I used the following to just enclose all numbers (integer or floating point numbers) in quotes:

json_decode(preg_replace('/("\w+"):(\d+(\.\d+)?)/', '\\1:"\\2"', $jsonString), true);