If you need to retarget .bvh from another source, you'll need to do this in another program. There are several options available.
The program I like to use it Motion Builder, which is an industry standard but it has a relatively high learning curve and is expensive. However, I believe you can get it free if you're a student, and if you have access to the educational discount you can get it as part of a suite for around $500 or so.
After we finish our current short film project, we're looking into using iClone5 Pro to create a short series of 'machinima' style movies, and this system can retarget and edit mocap from other sources (including iPi DMC.) To do this, you also need to get the 3DXChange Pipeline add-on. We got the total package last spring for around $500 - $600. We haven't used it yet so I'm not sure how it compares to Motion Builder for mocap retargeting and editing--from video demos I've seen, it seems pretty decent for the price. We'll probably get around to using it next spring. Will report what it's like using it when we do.
A few other 3D animation programs that can retarget 'outside' mocap data are XSI, Max, and Maya. I use Maya sometimes at work but I really don't know much about retargeting in Maya. In video demos I've seen, the procedure looks very similar to Motion Builder's system.
If you're on a tight budget, Blender may be a choice worth considering. I don't have any experience with it but I believe it has built in retargeting too--do a search, I'm sure there are videos showcasing this feature. I'm actually interested in Blender myself (one of my friends at work uses it for specific fx work,) but I don't have the bandwidth to learn a whole new 3D program these days. Maybe after my wife and I finish a few more movies.
Another option is
iKinema WebAnimate, which is a mocap editor in a web-browser. This is an online service where you can upload motions and your character, retarget, edit and check your results. I believe it's free up until you're ready to download the result. I've never used this service but I've seen posts from people who have reported satisfactory results. I'm not sure how much it costs to download from this service. (Maybe somebody who uses this service could post more details about it?) There are a couple of other online mocap services out there but iKinema WebAnimate is the one I hear about most often.
Hope this helps.
G.