The solution is not to turn your consultants in to sales people, or to attempt to coerce them into becoming an extension of sales.

As others have pointed out, this is how it works everywhere in the industry.

If you are a product company, and you have a consulting staff, you don't "pollute" them by having them also overtly serve the sales organization, you use them as your "feet on the ground" to gather intel about what is going on inside the customer account and to help you figure out how to best align your (sales) goals with what the customer is doing. A good sales person does not ask the people in the field to compromise themselves as trusted advisors to the customer, but they will try to figure out what is going on in the account in order to make the best pitch to the customer.

Easy.

What makes this sound like it won't be so easy for the OP is that he claims to work for an "IT consulting firm" not a product company. If you have a sales staff, like it or not, you're working a product company.