Microsoft RMS Dynamics 2.0 - Adding Standard items to a Matrix and setting dimensions for it.

We are trying to integrate our POS with our website. The website needs to show an item with two options. However, due to various reasons, these same items are single standard entries in the POS. For them to
show up on the website as 1 item with options they need to be matrixed in the POS.
I need to know if it is possible to create a Matrix item, then add a standard item to this Matrix and set a dimension for it.
I can currently create a Matrix item and add a standard item but I cannot set the dimension for it. I need to know if this is because I do not know how, or because it just is not possible.
Thank you for any help.
Best regards,
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