I am using the customer portal for clients to access some information. However they need clients log file upload in customer portal. However with licenses costumer portal only have access (read) the documents. They have some solution to send attachments from the customer portal?

I am using the customer portal for clients to access some information. The clients needs to be able to upload files in customer portal. 

However, with costumer portal licenses they only have access (read) to documents. Do Salesforce have some solution to attach files from customer portal?