I have a developer on my team who, while delivers good quality code, is significantly slower than the other developers on my team. This is causing a pretty serious bottleneck that I'm trying to find a way to resolve. In the medium to long-term, making the team cross-functional will allow other team members to help get velocity up, but I'm looking at any option I can to increase the output of this particular developer (especially since the project is at risk of going over budget).

This particular developer still likes to code "old skool". That is, he uses a text editor for coding, command line for every possible situation, and if given the chance to remove his mouse and any visual aids, he'd do it. He's explicitly clear: they want to do nothing but code, preferably where they have zero exposure to other humans, and preferably at home. Absolutely no meetings, no discussion, he wants the tasks that need to be done and to complete them by himself. Trying to introduce agile is going to be a challenge. He doesn't have many other responsibilities, 95% of his work is code.

Now, I'm not against developers refusing to use interfaces, mouses and IDEs if they want to make their own lives difficult (personally, I think it's just a show-off move, and slows development time significantly IMO), but when velocity is under par, I'm looking at this as one of the options to increase output.

So, the question is, is it fair and within my remit to ask the developer to switch up to an IDE to improve velocity? In my experience, this has a drastic improvement in time to complete a task, but I feel like it would be forcing him into a corner and taking away something he really enjoys, which won't help with motivation.

For those who say "it gives more flexibility/power!", I understand this point, and command line is always there for the 2% of time you need it. For the rest of the time, IDEs and visual interfaces were designed for a reason: speed and ease of use. I don't buy into it.

Edit: For clarity, I'm a new member to the team, brought on as a project manager, but I'm also an ex-lead-developer who has a significant amount more experience than the other developers in the team. I've been given carte blanche to make architectural and development decisions in order to recover this particular project which is in serious trouble, and is vital to the company's success.

Edit2: A common suggestion here is to ask the developer what he thinks will help improve his velocity. I've done this already a few times, but no useful response is forthcoming: "I'll think about it" which doesn't happen. That's part of the reason why I'm looking down relatively unusual routes to see if I can boost productivity in other ways.

Edit3: It's clear that the whole IDE/CLI discussion is unresolvable; both sides have their points of view, and like OSX/Windows, or Python/PHP or...there's no right or wrong way. If you want to have you say on this, head over to this discussion to continue talking to brick walls. The question wasn't if IDEs are better than CLIs, it was if I can ask this developer to try something new to see if it affects velocity. Ultimately, developers can code with punch cards or in Minecraft if they like, as long as the velocity is there. Please be aware that to become efficient with CLI has a much longer and more difficult learning curve than IDEs do, and it's possible that's the situation here.