I do this as well. I'll usually say things like "i appreciate it", and then when that starts to get difficult i switch back to "thank you". sometime's i'll add an extra syllable onto the front of it, so i'll say "uhthank you" or something to help me ease into the th sound. the extra syllable often goes unnoticed or people just think youre being funny, so ive never had someone point it out as long as you choose a syllable that sounds natural.