I am not familiar with that part of the Chesapeake, however here are some ideas based on doing some looking, and considering your endeavor.
You didn’t mention this resource, so I will offer it even though I imagine you know of it, but just in case:
Chesapeake Bay Access and Paddle-in Campsite Map – CPA Kayakers
Using that, there are soft launches about 6 miles north (Elms Beach) and south (Camp Lookout State Park) of St. Jeromes Creek, but none right at or in St. Jeromes Creek. Unfortunately nothing, hard or soft at that location, in terms of public launches.
If you need to land in St. Jeromes, then perhaps you could try contacting some landowners about a special use of their property. On Google Earth the St. Jerome Point looks like it has some potential, if the landowner was willing and happy to help the cause. The address, per Zillow, looks like: 16545 Saint Jeromes Neck Rd, Dameron, MD 20628
Another place that looks like it has potential would be prior to the mouth of St. Jeromes Creek: 16640 Saint Jeromes Neck Rd, Dameron, MD 20628. There appears to be some sort of public right of way just north of that lot, with a large sandy beach and undeveloped lots along that stretch of beach.
Drury’s Marina looks like it has potential too, though you will be using hard launches, not soft. It is just inside the mouth of St. Jeromes: 49768 Airedele Rd, Ridge, MD 20680
Hopefully someone with more knowledge of the local area will chime in with suggestions.