Using the % time spent on FogBugz tasks configuration parameter available under Time Tracking ->My Working Schedule you can configure how should the EBS algorithm allocate your working time on different projects when projecting your tasks' finish date.
All Other FogBugz Tasks
The default value is 100% on All Other FogBugz Tasks. This means EBS assumes you are working full time on FogBugz tasks. Meaning: it assumes that a task estimated for 8 hours of work you will complete during one business day (for the sake of simplifying our example we assume that you have configured 8 hours of working time).
If you change this to 25% (for example) EBS will assume that 8 hours of work will be completed by you in 4 business days, because you work only 25% (2 hours) of your working time on FogBugz tasks.
% Time per Project
You can refine this setting, by adding New % Time Allocation and setting how much of your time you spend on specific projects (in case you are working on multiple projects during the same period).
In case you have a team member that is very inconsistent in tracking their own time (for example he uses the time-tracking feature for about 25% of his time), EBS will reflect it by showing very wide bars for him on the Per-User Completion Dates chart.
Let's see possible workarounds for this case.
Option 1 - Changing % time spent on FogBugz tasks
If you would change his % time spent on FogBugz tasks setting to 25% on All Other FogBugz Tasks while his estimates are still correct you would distort your project delivery date estimates, by creating the impression that any task of his takes 4 times longer than estimated. Probably this is not the case if he delivers more or less as per his estimates, just he doesn't track his time.
These distortions would get "corrected" once he closes the 0 time cases (the ones where he logs no time). But since you don't know when he will do that, you will not know at a given point of time when are your delivery date estimates correct and when not.
Option 2 - Leave on the clock for one single task
If he would leave on the clock for one single case throughout the project, that would distort his velocity, resulting again in distorted delivery date estimates for any project he is working on.
The Best Solution
In case he is assigned to several projects, the options mentioned above would result in distorted estimates for several projects, thus probably impacting several teams.
The best solution would be to find a way to motivate the lazy developer to track his time more accurately. Some suggest as one way to achieve this is to provide paychecks with the same accuracy as him tracking his time.