idaX.exe -Otest:

• test – DLL inside Ida’s plugins directory (with the appropriate filext DLL, PLW, P64)
• idaX – ida[wtq](64)? depending on the version

btw. Ida says:

Loading plugin C:\ida\plugins\test.plw… C:\ida\plugins\test.plw: incompatible plugin version, skipped

for my malformed IDA Plugin test dll but the DLL is loaded nevertheless.