Show Text area if Custom Size is selected

Hello,

Just wondering if the following is possible without too much coding ...

We sell clothing and currently have set up Size options like Small, Medium, Large and so on.

I would like to add "Custom" to the list and once someone selects it , the text area box should appear, under the size options, for them to enter their custom size.

I tried to show the text area with the size options together but it doesn't look elegant at all and it might confuse customers if its there all the time...

So the idea is to keep the text area hidden when someone selects size Small or Medium etc and show the text area when someone selects Custom from the Size options.

Any other way to accomplish this without changing the code?

Thank you!

anyone?