Calendar Widget displaying posts by custom field (date)

I created a website build around a custom post type events. These events have custom fields, one of them is the event-date (the date the event is happening, NOT post publish date). I’d like a calendar widget that simply highlights the days an event is happening (maybe with a link to it). This means i need to plug my custom fields into a calendar widget plugin.

I found this post from 2 years ago, http://wordpress.org/support/topic/display-posts-in-a-calendar-using-custom-field-as-date?replies=8 – it seems they wanted exactly what i’m asking for. Unfortunately i couldn’t figure out how to do it with the plugin mentioned by them (FT calendar).

Most calendar widget plugins simply use the pust-publish date. I need them to take their date-data from a custom field. Do you guys have an idea which calendar-widget-plugin/way would be best for me?