My question would be can you even find the bulbs for sale now? I really don't think planting your bulbs will bother your perennials. They won't have spread much in the next couple of months and the bulbs will be put in spaces between them I imagine. Bulbs look far better in clumps than individually so you could leave gaps for them if you are concerned. Plant with a narrow trowel (you can buy a bulb trowel) and I'm sure your perennials will be fine. I garden between mine all the time. I just thought of something else ... the watering needed by perennials planted in July would not agree with the bulbs. In the Autumn the watering will have reduced.

If you live in Boston, now is NOT the time to plant those bulbs. They have to make roots in fall and then be subjected to a winter's cold dormancy period.