T-SQL (SS2K8) :: Parsing A String

I have a table Alert_Types with these fields :

alert_id,
alert_source,
body,

Now whenever a new alert is registered record goes in table like

alert_id = 1,
alert_source= document_detail_view,
body = Document ID: @document_id
Customer Name: @customer_name
Item name: @item_name
Quantity: @qty

it was simple to parse simple variables using replace functions. eg. REPLACE(@str, '@customer_name', @customer_name). It worked like mail merge.the converted string was then sent forward using a webservice.now my requirement is to add conditional values in body field e.g:

body = Document ID: @document_id
Customer Name: @customer_name
Item name: @item_name
Quantity: @qty
IF isnull(@rate, 0) > 0 Rate: @rate
IF isnull(@rate, 0) > 0 Amount: @amount

how can i parse strings like this. I'm open to change format of values for body field.