Juniper berries substitute for roast pork shoulder?

An old world standard, simply pierce with pointed knife to various depths into the roast; force your finger into the hole to open it; push a clove and sliver of garlic into the hole with some almond oil on it. You can also add or sub rosemary sprigs with the other spices. Then baste and roast as usual. The spices melt into the meat and develop an exquisite savor.

Divide and conquer?
Omit the juniper berries from the roast, so them as don't like the taste can avoid, but include them in a sweet-sour preserve.
Preserves or chuntey with apricot and juniper (old John Willoughby and Chris Schlesinger recipe, lost now, but basically a little sugar, lemon juice, juniper berries and - in winter - dried apricots).
Rhubarb (in freezer case in winter) recipe here
http://www.kitchenhealssoul.com/2014/06/09/rhubarb-juniper-berry-jam/html
If you have leftovers, stick them in the fridge for other parts, cheese boards, etc.

Whole allspice might work....just spit-balling here. I think that's where I would go - flavor would work with a roast pork shoulder.

I suggest you simply omit the juniper berries and carry one with the rest of the recipe.

One could substitute another spice like Szechuan peppercorns for the juniper berries, but there's no telling if your dinner guests will appreciate that flavor.

The easiest approach for tackling holiday dinners like Thanksgiving and Christmas is to keep it simple. In any case, it sounds like your dinner guests will still have turkey as the main course.

No one can please everyone all the time (and that comment isn't specific to culinary dishes) so another option is to follow the recipe as is and let the juniper berry haters eat something else.

Good luck.