Importing Invoices with comments

I am working on automating invoice generation with Sage, 

when i create a invoice with .imp file how can i add a comment on the invoice?

for example if i sell a perticular item, we often add on a seperate line in the description field a comment like "subscription valid from April1st to March 30th."

but when doing a Sales inovice though imp i'm not sure if its possible.?