[inksticks]

I figured out a good solution. Here it is:

In /mail/html/order_invoice.tpl change the following

{$lng.lbl_payment_method}:
{$order.payment_method}

to

{$lng.lbl_payment_method}:
{$order.payment_method|truncate:18:""}

You can adjust the truncate value as you wish but I found that 18 was a good value because it allows all payment names up to 18 characters long to be fully shown on the email but when a name like Credit Card (AuthorizeNet: AIM) is used it will only show the words 'Credit Card'

Using the truncate command with :"" after it as above will round to the nearest full word so that you will not get partial words listed on your invoice.