Using less variable inside microsoft gradient

I'm having some trouble getting .LESS to recognize that there is a variable in a string. Here is my current code

filter: progid:DXImageTransform.microsoft.gradient(startColorstr='@{startColor}', endColorstr='@{endColor}', GradientType=0);

@startColor and @endColor are both variables.

How can I place a .LESS variable inside a string?

EDIT:

I fixed it (I think..) Here is the end code that works for me

filter: progid:DXImageTransform.Microsoft.Gradient(startColorstr=@startColor, endColorstr=@endColor, GradientType=0);