I like to use a frame bag like this…

…but there’s no stem as such with a Lefty for that front strap to go round.

What I want is a long is a long, low bag, say 250x50x50mm that fits on the top tube with some means of stopping it rolling round, velcro probably, so that I can grab food out of it easily while racing.
I’m sure BeerBabe could make me something, I just thought I’d see if there’s a ready made option out there

Stopping it rotating without the attaching to the steerer is going to be difficult.
Velcro on the top tube and on the bottom of the bag?

Fit it at the rear of your top tube and wrap it around the seatpost.

what Geoff says, just don’t use the stem strap and sticky-backed velcro off eBay on TT and bag.

Alpkit stem cells or feed bags would be better in that situation for grabbing things on the go.

It seems I am not the first to think of this and they even put threaded bosses on frame top tubes to take the bags.
http://www.mytriathlon.co.uk/xlab-aerodynamic-frame-storage-stealth-pocket-300-2-5-high-20-cu-ins-insulated-top-tube-bolt-mount/

Yes, without drilling my frame, I was planning on gluing velcro to the top tube.

Fit it at the rear of your top tube and wrap it around the seatpost.

I’ve tried that before and it’s a good compromise.
I’d prefer to have it nearer the front if possible. Now that I know there are bolt on ones for triathlons, I’m surprised there aren’t simple velcro on ones for those who haven’t got a drilled frame.

Sticky backed Velcro to your frame?

What about a piece of stiff webbing on the front, trap this in the gap in the stem where the pinch bolts are (provided your stem has rear pinch bolts)or even a longer tab with two holes that align with the bolt holes holding the front of the bag secure. Hope this makes sense!

Sew a tri-bag onto the top-tube panel of a Jandd frame bag?