Charcoal whitening with attachments. Is this OK to do?

I have Invisalign and have lots of attachments (appropriately 20, inc front teeth) and although the Invisalign so far is doing the job of straightening my teeth, I am so self conscious that my teeth are so discoloured. I will get free Zoom whitening at the end of my treatment but this is still a long way off. I have seen some charcoal teeth whitening advertised and would like to give it a go. Is this ok to do with attachments? If not, is there anything else you can suggest please? Thankyou