Maybe the guitarist is playing too much when he is not soloing and so losing too much when he drops it.
As for the bass:
Have a variant of the bass line for the instrumental section so instead of being empty it just sounds different - in fact instead of being the guitarist soloing, treat it as an instrumental section.
If you were playing quarter notes then play eighths, or vice versa.
If you were pedalling then walk, or vice versa.
If you were walking up then walk down, or vice versa.
But space is good. Most of us play more than is necessary.