buy a filler called mili put,I use it all the time for similar things,its a 2 part filler so you have to mix both parts together in your hand,so make sure your hands and the hole your filling are clean or it will look off white,fill your holes,sand down with wet and dry paper then buff up with a upvc cream cleaner,hope this helps
shaun www.sdwupvcrepair.co.uk, October 2008