I don't fully understand what you mean by front-end digitisation. In the IT world, it's development of the interface/design/customer journey of a tool and/or product.
Having said that, I believe that all consulting companies are involved in this now, as Marco has explained in his answer. For example, an MBB firm might be engaged to analyse what insurance and banking products are missing at the moment, and asked to help come up with a list for the client. This list can then be used to create the new insurance and banking products that were only meant for digital distribution channels. A hypothetical example could be, a one-day insurance for your apartment if you were renting it out on Airbnb. Then, they might also advise the customer about possible partnerships, so in this hypothetical example, a bank might partner up with Airbnb to offer the insurance directly on the Airbnb platform.
Overall, the whole digitisation thing has taken consultancies by surprise and so many are putting high efforts to recruit people who have Digitization background. But based on what I know, I would say that Accenture has the best position at the moment.
Have a look at this article as well: https://www.forbes.com/sites/falgunidesai/2016/03/23/the-rise-of-digital-consultancies/#217f88776a79