In most of these "no poach" scenarios I think the legalities are such that a firm can be forced to agree not to actively approach candidates within a client organisation - ie. not headhunt them out or entice them to leave. But if the candidate makes a direct application to the firm - or responds to an advert in the press - then the firm would be obliged to give the candidate due consideration and not dismiss them out of hand purely because they come from a client organisation.
One innovative approach to consider would be to approach your current employer and ask if they would consider placing you on secondment with the consulting firm. The consultancy might well oblige with a secondment to keep the client happy, but in the process you get the chance to experience the consulting lifestyle without having burnt your bridges with your existing employer.
Employers are keen to ensure that there is as much "knowledge transfer" as possible from the consultants to the client employees, it's now a major purchasing criteria when choosing which consulting firm to engage on a project. More knowledge transfer means the client is less dependent on the consultancy in the future. Positioned correctly, the suggestion of going on secondment could be seen as a fantastic way of achieving this "knowledge transfer" and therefore be in the interests of both the business and you personally.
Hope this helps and good luck.