Long trill

What I want is to create a long trill on -let's say- a "Do" that lasts throughout a whole measure.
I take the following steps:
1) Create consecutive demi-semiquavers of Do and Re in voice 1 throughout the measure.
2) Make the above notes invisible.
3)Write down only one semibreve note of Do with the symbol of the trill above it, in voice 2.
In this way the score appears nicely and as it should considering notation matters, while it is played back as a real trill.
The problem is that the measure stays unproportionately wide (because of the hidden 1st voice). Is there a way I can reeeally squeeze it? I don't care if the hidden notes get crowded, since they are invisible. I' m trying my best with what I can (measure properties, etc.), but it won't shrink enough.
Any advice?