Leaky Valve seals won't do any major damage.
You can drive like that for a little while. The ony drawback I know of are:
1. Constan lose of oil, so you have to make sure it doesn't run out of oil.
2. Contaminated spark-plugs, which might cause a misfire.
3. Carbon Build up on Valves and Pistons.
Leaky valve seal have one "benifit". Since the oil leaks inside the compression chamber you will get a better compression and little more power
. Although it's nothing major and probably very minimal.
If you want a temporary fix, you can get any "No Smoke" additive from Canadian Tire or used thicker oil, like 10w40 or 15w50 or switch back to Regular oil if you are using synthetic.
Art