Sounds like quite a feat, eh? It's not quite that once you give it some thought and try it out. And to help you along, we will describe some ways and have taken some photos to illustrate how you keep the Pump Funnels on. Do note that we've taken photos only on one side. You can do this with BOTH funnels on - one funnel on each side.
*do click on the thumbnail photos for larger views*
Method 1: Re-do Bra Cup flap

Bring the bra cup flap around the bottom and side of the pump funnel, then re-clip your bra cup back to hold the funnel in place. Have it positioned well and once you turn the pump motor on and running, the funnel will stay in place! This works for BOTH bras with the top-clip styles and the centre-clip styles (yes, I've tried it myself!).
Method 2: Use rubberbands

Use rubberbands to hook onto the bra clip. This can only work with bras that have
top-down drop-cup flaps. I have not personally tried this method, but some mothers say it works well for them!
Method 3: Use a Tube Bra
Just cut 2 very tiny holes in the tube bras where the funnels can be placed into when you wear the tube bra. The above 2 methods allows you to adapt using whatever nursing bra you are wearing that day. For this tube bra, you'd need to specially bring this along with your pumping equipment, so you'll have to be the judge as to whether you'd find this convenient!
Try either of the methods and let us know how it works for you!
Or if you have other ways or tips, do share them by clicking on the "Comments" below to enter your own experiences!
The handsfree pumping online photo album is at:
http://www.flickr.com/photos/momsinmind/sets/72157594324905453/