Urgent Schengen Visa. Help needed

Hi,

Currently working in the UK. I have a conference in spain on the 28th of June and the earliest appointment date I could get from the spanish consulate is on the 23rd of June. This is way to risky as I'm unlikely to receive my passport back before the 26th.

What are my options please??
I have been able to get an appointment straight away for tuesday (1st July) with the netherlands consulate but don't know how I can play this. My flights are booked already and go from LHR directly to spain.
I also have a letter from my employer about my going on the conference in spain and bla bla bla. I just can't get any invitation letter from Holland - which will make getting a business visa via holland tricky. Any advice please? Time's ticking