V.B.
Oohhh... I don't think I would be doing any stretches until you get the okay from your doctor. Not with a tear. If you just pulled it or strained it... then yeah, ok. But with a tear and you are in a boot? I'd get the go-ahead from the doctor before I did any stretching. You don't want to do any additional damage while the tear is healing.
Technically, Plantar Fasciitis is little small tears.... but they don't put you in a walking cast for that, normally. Sounds like you have a more severe injury, a completely torn ligament... If I am wrong, there ARE stretches and things you can do to help with plantar fasciitis. But tearing the tendon is not "just" plantar fasciitis and I would be very cautious about doing anything your doctor hasn't suggested or approved.
But I don't know why you couldn't ice it to help with any pain...