A few stretches for weightlifting that I am using at the moment.
To improve the squat. Sit somewhere comfortable and, keeping your heel on the floor, drive your knee forward so the ankle is maximally dorsiflexed. Now put some weight on top of the thigh to aid the stretch. 20-30kg does well for me. You can contract-relax here or just sit it out. Its not too painful or awkward as stretches go, so is good for long periods sat in front of the TV. In fact, I'm doing it as I type.
Thoracic Mobility and Posterior Capsule Stretch
You need a foam roller and a disc for this one. 10kg is a good start, graduate to 20 or 25 as your mobility improves. Prepare for some pretty impressive crunching noises as well. Basically, lie on the foam roller, and imagine melting your upper back over it, extending as much as possible. Relaxed, deep breaths in and out and help open up the ribcage as well. The weight can be held on the chest, or out in front on straight arms to get a sly posterior gliding stretch at the same time. Work slowly up and down your upper back to open it up. Good for the overhead position
An exercise borrowed from the bodybuilders, but great for opening up the thoracic spine and stretching out the overhead position. Lie on the foam roller again and grab a light plate, 2.5-10kg is plenty. Tighten the abs, melt the thoracic spine over the roller, then lower the plate to the ground, pushing your head through as in a good jerk receiving position. Keep the arms straight and squeeze the shoulder blades down and back. Hold for 2, then pull back and repeat for reps.
Flexibility is paramount for weightlifting and I know as well as anybody that I don't have enough and need to work on it more. Stretching sucks, everyone hates it, but it's gotta be done. Do these at home in front of some good TV (not Britain's got talent, a complete misnomer judging from what I've seen) and improve your lifting.