Sending form array values to remote server via Xhr

Hi there, I'm encountering some problems trying to submit an original html form array to a remote web server PHP page via xhr POST method.

As an example, I need to submit the following form:

<form method="post" action="http://www.mysite.com/">
    <input name="option[123]" value="205">
    <input name="option[124]" value="409">
    <input name="otherparams" value="1">
...
</form>

so the only way I found to manage this is the following code:

var client = Ti.Network.createHTTPClient({
    onload : function(e) {
        Ti.API.info(this.responseText);
    },
    onerror : function(e) {
        Ti.API.error(e.error);
    },
    timeout : 100000  // in milliseconds
});
client.open("POST", url);
client.send({'otherparams': 1, 'option[123]': 205, 'option[124]': 409});

where the PHP page (with a print_r($_REQUEST)) returns

Array
(
    [otherparams] => 1
    [option] => Array
        (
            [124] => 409
            [123] => 205
        )
)

now the problem is, how can I dinamically build my object? As an example, any way I tryed to make something like

...
var mynumber1 = '123',
mynumber2 = '124';
client.send({'otherparams': 1, 'option['+mynumber+']': 205, 'option['+mynumber2+']': 409});
 
/* OR */
 
var myObj = {};
    myObj.otherparams = 1;
    eval("myObj.option["+mynumber+"] = 205;");
client.send([myObj]);

unfortunately failed...

Does anybody alredy realized how to do that? I absolutely cannot change the way my server manage requests parameters...

Thanks in advance to everybody...