Configuration of burndown chart ideal line with planning of total available hours in the sprint

We need a possibility to have some time sheet for calculating total available hours for people during the sprint, like the one you can see in the attachment. This sheet could be similar to an already existing JIRA Timesheet Plugin (https://studio.plugins.atlassian.com/wiki/display/TIME/JIRA+Timesheet+Plugin), but must be editable.

We have used this in our sprint backlog planning with Excel, because some of the people in the team are not available or partially available on some of the days during the sprint (because of day offs or any other reason) and this sheet just reflects that. With this information we are able to estimate more accurately and calculate the total amount of available time.

Furthermore we are able to draw the ideal estimate line closer to the reality (see attachment), which shouldn't be just a straight line as it is currently in the GH. For example if you have a two week sprint and you know that half of the team is unavailable on the first week for any reason, then there's no way you can match the ideal line and also you don't know whether you are right on track or not. With the ideal line reflecting the exact amount of time available on particular day, you are able to keep track on the progress whether you are meeting the schedule or not.

We're certainly missing such functionality here and this prevents us (Blocker priority) from switching from Excel+Bugzilla to JIRA+Greenhopper. Is there any way to implement this?