java - How to effectively blur a single object in a scene with GLSL? -

i'm trying blur object in scene glsl shader.

what when i'm drawing scene, may reach object needs blurred. when do, in 2 passes (from understand more optimized doing in single pass).

so draw object off-screen fbo (transparent bg) horizontal blur. draw fbo screen's default fbo vertical blur.

this result (method #1 in image):

the white "glow" problematic. however, if draw object off-screen fbo not have transparent bg, correct blur result method #2 in above image. however, have white bg behind object - not good.

what i'm asking how supposed blur two-pass approach if can't use transparent-bg fbo? or there trick can fix this? maybe mess blending src/dst functions?