need more loader lift

I bought a 5065e to off load wood burning boiler from a flat bed semi and to have a hoe attachment for installations

Small problem I have is that the largest boiler is about 100 to 200 pounds too heavy. I wont sell or see many of these but I have to have the equipment to remove them from the truck. Can I modify the pump of relief valve to gain a bit more pressure?

My loader is a 553 and I know someone is going to say I will blow out my seals. I dont believe they are rated at the ragged edge of their ability and I dont care to be hard on my equipment.

Thanks