Why do you want to add that? Everyone knows 1 satoshi is 0.00000001 Bitcoin.
Will you please tell me how much satoshi i can buy with 5.7$(current btc price)?Can you do it without calculator?
Ok. I undestood your question wrong. But it is still about decimals. You can use for example
http://btcwidget.com/ and tell users how to change decimals for getting right amount in satoshi.